US3831157A

US3831157A - Spring loaded power source for intrusion alarm

Info

Publication number: US3831157A
Application number: US00349738A
Authority: US
Inventors: J Wiegand
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-04-10
Filing date: 1973-04-10
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20

Abstract

A magnet is mounted for snap action movement between first and second positions. The magnet is spring loaded into a normal first position. The event causes the spring to move the magnet sufficiently so that the magnet rapidly switches into its second position. This switch of the magnet changes the direction of flux through the core of a coil thereby generating a pulse to the output of the coil. This pulse is applied as the power input of an oscillator to generator a pulse of a radio frequency signal for transmission. A super regenerative receiver tuned to the oscillator frequency is normally on producing a noise output that provides a signal for maintaining a relay on or energized. As long as this relay is on an alarm is maintained off. Receipt of the radio frequency pulse by the super-regenerative receiver quiets or quenches the output of the super-regenerative receiver thereby removing the signal that causes the relay to be maintained energized. The relay becomes deenergized and the alarm is set off.

Description

United States Patent [191 Wieg and [111 3,831,157 [451 Aug. 20, 1974 SPRING LOADED POWER SOURCE FOR INTRUSION ALARM [76] Inventor: John R. Wiegand, 101 E. l-lathome,

Valley Stream, N.Y. 11580 22 Filed: Apr. 10,1973

21 Appl. No.: 349,738

[52] U.S. Cl 340/224, 340/164, 325/66,

325/185, 325/428 [51] Int. Cl. G08c 17/00 [58] Field of Search 340/224, 164; 325/119,

325/161, 169, 185, 350, 428, 429, 318, 392, 393, 364, 66; 310/750, 75 R, DIG. 1; 331/66, 116, 185;317/140, 146, DIG. 1

[56] References Cited UNITED STATES PATENTS 2,800,104 7/1957 Cameron et a1. 325/66 3,119,065 1/1964 Blake 325/428 3,230,455 l/l966 Kostam. 325/185 3,283,315 11/1966 Frear 325/364 3,487,398 12/1969 Rieth 331/185 3,614,760 10/1971 Zimmet. 340/224 3,621,398 11/1971 Willis 325/185 Primary Examiner-John W. Caldwell Assistant Examiner--Richard P. Lange Attorney, Agent, or Firm-Ryder, McAulay, Fields, Fisher & Goldstein [5 7] ABSTRACT A magnet is mounted for snap action movement between first and second positions. The magnet is spring loaded into a normal first position. The event causes the spring to move the magnet sufficiently so that the magnet rapidly switches into its second position. This switch of the magnet changes the direction of flux 7 through the core of a coil thereby generating a pulse to the output of the coil. This pulse is applied as the power input of an oscillator to generator a pulse of a radio frequency signal for transmission.

A super regenerative receiver tuned to the oscillator frequency is normally on producing a noise output that provides a signal for maintaining a relay on or energized. As long as this relay is on an alarm is maintained off. Receipt of the radio frequency pulse by the super-regenerative receiver quiets or quenches the output of the super-regenerative receiver thereby removing the signal that causes the relay to be maintained energized. The relay becomes deenergized and the alarm is set off.

12 Claims, 6 Drawing Figures PAIimmwnzomn sum 10F 91 Q RVO PATENTEBAUGZOISM SHEET 20$ 3 SPRING LOADED POWER SOURCE FOR INTRUSION ALARM BACKGROUND OF THE INVENTION This invention relates in general to an alarm system and more particularly to one having a sensortransmitter which requires neither an outside source of power nor battery yet provides a signal that the system receiver can employ to generate the alarm.

There are a wide variety of intrusion alarm systems which can be adapted to serve many different purposes. It is difficult to compare these various systems because of the divergent cost considerations, environmental applications and tradeoff requirements between false alarming and sensitivity. However, in general, there is an increasing requirement for inexpensive, reliable, long-life systems in which the chance of a false alarm is minimized and the assurance of an alarm upon intrusion is maximized.

Accordingly, it is a major purpose of this invention to provide an intrusion alarm system in which these frequently contradictory use parameter are optimally met while maintaining the cost of the device as low as possible.

It is a particular purpose of this invention to provide a sensor device at the intrusion area which is not dependent either on power supplies, remote or local, such as house current or a battery. Thus malfunctions in a power supply will neither decrease reliability nor increase risk of false alarming. Further, the non-use of a power supply reduces the ability of an intruder to disable the system.

U.S. Pat. No. 3,614,760 issued on Oct. 19, 1971 teaches one technique for generating a signal without requiring a local source of power. The technique employed therein is to move a magnet past a coil and thereby generate pulses of current at the output of the coil. The pulses of current are then used on the power input to an oscillator to provide a series of pulses of radio frequency energy for transmission to a receiver and alarm. However, the greater the amplitude of the output pulse from such a coil, the better can be the trade off between range, sensitivity and false alarming.

Accordingly, it is a further purpose of this invention to provide an increased amplitude of output pulse from the sensor-generator.

It is a further purpose of this invention to provide the above purposes in a design in which the sensor automatically resets and thus does not require operator or owner access to the sensor location to place the system in a condition ready to respond to the next alarm producing event.

It is another purpose of this invention to provide a system which is adaptable to provide an alarm in response to various events so that the basic system could be adapted to an intrusion alarm, a fire alarm or some other event responsive alarm.

BRIEF DESCRIPTION OF THE INVENTION In brief, this invention includes a sensor-transmitter that employs in combination a mechanical snap action to electrical pulse transducer and an oscillator to provide a pulse of radio frequency energy that has a substantial magnitude. Because of the transducer, the sensor-transmitter requires no source of electrical energy.

Upon occurrence of an event, such as the opening of a door or window, a spring loaded arm moves a magnet rapidly from a first position to a second position. In its first position, the flux of the magnet passes in a first direction through the core of a coil. In the second position, the flux of the magnet passes in a second and opposite direction through the core of the coil. The magnet is held in each of its two positions, by virtue of magnetic attraction, against an iron flange of the bobbin on which the coil is wound. Accordingly, the force required to switch the magnet from its first position to its second position has to be greater than a certain threshold. Once that threshold force is exceeded the magnet is caused to break away from its first position and thus rapidly moves to its second position at which point it is held in that second position by magnetic attraction against the iron flange. The reversal of the flux through the core induces a pulse in the coil that is applied as a power input to the oscillator to provide an output signal having a predetermined frequency.

A super-regenerative receiver :is tuned to a carrier frequency equal to the frequency of the output signal. The normal noise output of the super-regenerative receiver provides a holding signal for a first relay. The relay contacts are open when the relay is unenergized. Thus, when in the system, the first. relay is normally energized and its contacts held closed by virtue of the rectifier output. When the alarm condition generates an output signal from the sensor-transmitter, the superregenerative receiver picks up the signal and the unmodulated carrier frequency quenches the superregenerative amplification. As a result, the output of the super-regenerative receiver is quieted thereby eliminating the holding signal for the first relay. The first relay becomes de-energized and reverts to its unenergized state with its open contacts. The opening of the contacts de-energizes a second relay to switch the state of the contacts of the second relay and thus complete a circuit to an alarm thereby turning the alarm on.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram in partial schematic of a system embodying this invention.

FIG. 2 is a perspective view in partial phantom of the sensor-generator employed in the transmitter portion of the FIG. 1 system.

FIG. 3 is an exploded view of the FIG. 2 generator.

FIG. 4 is a view of the top of the magnet of the FIG. 2 generator showing the two positions of the magnet, Position A being the normal position and Position B being the position in response to an actuating force.

FIG. 5 is a sectional view in partial relief showing the mechanical engagement between magnet and the mechanical arm for switching the position of the magnet in response to an alarm condition.

FIG. 6 is a schematic diagram of the receiver-alarm portion of the FIG. 1 system.

DESCRIPTION OF THE PREFERRED EMBODIMENT The System FIG. .1 illustrates the system of this invention. The sensor-transmitter portion of the system includes a pressure actuated snap action generator 12 whose output is applied to an oscillator 14. The structure and operation of the snap action generator 12 is described in greater detail in connection with FIGS. 25.

The frequency of oscillation of the oscillator 14 is determined primarily by the capacitor C1 and inductor Ll, the frequency in one embodiment being 290 megahertz. The inductor L1 is illustrated in FIG. 1 in the format that appear on a circuit board. When so laid out on a circuit board, the inductor L1 operates as the transmitting antenna. The transistor Q1 and the associated circuitry form a standard type of oscillator including an inductor and capacitor used for feedback.

The receiver-alarm portion includes an antenna 16, a super-regenerative receiver 18, a relay arrangement 20 and an alarm 22. This receiver-alarm portion of the system is described in greater detail in connection with FIG. 6. It might be noted at this point that the normal noise output of the super-regenerative receiver 18 is used as a hold-in current for a first relay that has open contacts when unenergized. As a consequence, the relay is energized under the non-alarm condition of the system and the relay contacts are maintained closed. Upon receipt of an alarm signal, the super-regenerative receiver 18, which is tuned to the frequency of the transmitted signal, is thrown into its amplifying state at which point the output of the receiver 18 quiets so that the relay is deenergized and its contacts open thereby opening a circuit which switches the state of a second relay and causes the alarm 22 to go off.

The Pulse Generator As shown in FIGS. 2 through 5, the source of power is a snap action generator 50 which converts mechanical energy into electrical energy through the medium of a rapid change in magnetic flux. This generator unit 50 does not require an outside electrical source such as house current nor does it require a self contained electrical source such as a battery. Thus the power generator cannot be defeated by cutting electrical lines; nor will it deteriorate with time as occurs with a battery which has a shelf life.

In the generator 50 illustrated, an electrical coil 52 is wound on a low reluctance iron bobbin 54. The coil 52 has a large number of turns (5,000 in one embodiment). The bobbin 54 includes a core 56 and first and

second iron flanges

58 and 60. These

iron flanges

58 and 60 extend beyond the coil winding 52 itself so as to attract the poles of the pivotable magnet 62 for reasons described immediately below. A magnet 62 is pivotally mounted to frame 64 to permit rotation about the point 65. The frame 64 contains the magnet 62 as well as the coil 52 and bobbin 54 arrangement. When pivoted to one end position, (position A in FIG. 4) the magnet 62 has its north pole in contact with the inwardly facing surface of the flange 58 and its south pole in contact with the inwardly facing surface of the flange 60. In the other end position (position B in FIG. 4) the pole positions are reversed with respect to the flanges with which they are in contact. In both end positions, the flux from the magnet 62 is coupled to the coil 52 through the core 56. However, the direction of the flux through the core 56 reverses when the magnet 62 switches from one end position to the other end position. This complete flux reversal through a coil 52 having a large number of turns means that a substantial change in flux-turns occurs each time the magnet 62 is pivoted from one end position to the other end position. In order to maximize the value of the change in flux-turns, the magnet 62 preferably has a shape, such as is shown, which conforms to the surface of the coil 54 and reaches to the

flanges

58, 60, so that a low reluctance path is provided through the core 56 and thus a maximum amount of flux is coupled to the coil 52. To assure this low reluctance path, the

iron flanges

58, 60 are in contact with the iron core 56. Accordingly, when in the end positions A or B, there is no air-gap in the low reluctance path through magnet 62, flange 58, core 56 and flange 60.

The frame 64 is a non-ferrous resilient metal such as aluminum. The edge 68 of the side 70 is integral with the adjacent side 72 but the other edge 74 of the side 70 is free and spaced from the rest of the frame 64 so that the side 70 can pivot about the edge 68 and can be pressed inwardly by at least a certain predetermined distance. An arm 76 extends from the side 70 along a groove 77 cut out of the side 78 and connects to the magnet 62 at a point offset from the pivot point 63. Thus when the side 70 is pressed inwardly, the arm 76 causes the magnet 62 to rotate about its pivot point 63 from the normal position A to the position B as shown in FIG. 4. Because the magnet 62 is held attracted to the

iron flanges

58, 60 in the normal position A, a certain minimum force is required on the side 70 to break that magnetic attraction and cause the magnet 62 to pivot. Once that force is achieved the magnet 62 will break free of the magnetic attraction to the

flanges

58, 60 and rapidly pivot past its center line to be attracted to the flanges in the B position. Because of the force on the side 70 and because of the attraction of the flanges, the movement of the magnet 62 will be a snap action. Thus, the magnetic force betwen magnet and flanges provides what is equivalent to a toggle action and assures a rapid switch from one extreme position to the other extreme position. Furthermore, it assures that this switch occurs not only rapidly but within a predetermined time period. As a consequence, the change in flux-turns per unit of time is not only substantial but is substantially repeatable.

In addition, the resilient parameter of the frame material assures that as soon as the force on the side 70 is released, the side 70 suddenly will spring back to its normal position bringing the magnet 62 back to its normal position. In many alarm and other uses the springback will generate a second pulse which can provide a degree of redundancy and assurance that the receiver will be appropriately triggered. In any case, this design has the very important function of negating any need for a reset step. This design provides automatically resetting once the actuating force is removed.

Accordingly, as can be seen from the above description, the pulse generator 50 is a simple, inexpensive, rugged, self-contained unit that provides repeatable predetermined output pulses and has an automatic reset feature.

The Receiver-Alarm FIG. 6 illustrates the receiver alarm portion of the system. As shown in FIG. 6, an antenna 17 provides an input signal which is coupled through inductors L2, L3 to the base of transistor Q2. Ambient noise as well as the internal noise of the transistor Q1 are coupled to and amplified by transistors Q3 and Q4. Although two amplifying transistors Q3 and Q4 are shown, only one is necessary for the operation of a super-regenerative circuit. Both of these transistors Q3 and Q4 are biased to operate in the known super-regenerative faction thereby providing a very high amplification and a significant noise output level which in turn is applied to the base of the transistor Q5.

The transistor Q5 operates unbiased and thus essentially conducts only on the negative portion of the input noise signal. As a consequence, the output from O5 is unidirectional to provide a bias on the base of the transistor Q6 and maintain the transistor Q6 conducting essentially continuously so that the relay RYl is continuously energized and the relay switch arm S1 is held closed. As long as the arm S1 is closed (as shown), current is applied to the relay RY2 to hold its switch arms S2 and S3 in the state shown. The arm S2 operates as a holding circuit and the set button 80 has to be actuated initially in order to complete a circuit to initially energize the relay RY2. After being actuated, the set button 80 is released and the arm S2 remains as the holding circuit shown. Only when the arm S1 opens will the relay RY2 become de-energized so that the arm S2 will switch from contact'A to contact B. The switch arm S3 is held against the contact C by the energization of the relay RY2. When the relay RY2 is deenergized, the arm S3 switches over to the contact D thereby completing a 24 volt circuit through the alarm 22. One alarm that may be employed is the Sonalert alarm, manufactured by Mallory as part No. SC628. But any one of a number of different portable or other types of alarm devices can be employed.

The unit 82 has a 24 volt input and employs a volt zener diode Z1 to provide a stable 10 volt output as the supply voltage for the transistors in the super regenerative receiver 18.

The battery 84 is a standby power supply that is used when and if line voltage fails. As shown, the diode bridge 86 rectifies the output from the secondary of the transformer T1 in order to provide the 24 volt DC power required for operation of the relays RYl and RY2 as well as to provide the input to the unit 82 which in turn provides the 10 volt DC power required for the transistors. If this line voltage fails, the relay RY3 will become de-energized thereby switching the switch arm S4 from the position shown (contact E) to contact F which will connect the battery 84 to the arms S4 and S3 so that power can be made available for the alarm 22.

What is claimed is:

1. An alarm system comprising:

a coil a permanent magnet positioned with its flux coupled to said coil,

said magnet being mounted for snap action movement between a first position and a second position,

said flux of said magnet being coupled to said coil in a first direction when said magnet is in said first position,

said flux of said magnet being coupled to said coil in a second direction when said magnet is in said second position, said second direction being substantially opposite from said first direction,

said snap action movement of said magnet inducing an output pulse from said coil,

a radio frequency oscillator circuit energized solely by said pulse to provide a substantially unmodulated radio frequency output signal having a predetermined frequency and a duration substantially determined by said pulse,

a super-regenerative receiver within radio transmitting distance of said radio frequency signal, said super-regenerative receiver being tuned to said predetermined frequency, said receiver being quenched by said signal, and

relay means coupled to the output of said receiver and responsive to the state of said receiver to switch from a first state to a second state when said receiver is quenched for more than a predetermined time period, said duration of said pulse being greater than said predetermined time period.

2. The system of claim 1 wherein said relay means comprises:

a first relay having a first contact that is open when said first relay in unenergized and closed when said first relay is energized, said first relay being energized by said output of said super-regenerative receiver,

a second relay having a holding; circuit that includes said first contact of said first relay, said first contact when opened breaking the holding circuit and deenergizing said second relay, said second relay having a second contact that is open when said second relay is energized and closed when said second relay is de-energized,

alarm means connected to a source of power through said second contact of said second relay.

3. The system of claim 1 further comprising:

first and second ferro-magnetic stops,

said permanent magnet having first and second ends,

said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop,

said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop,

and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferromagnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

4. The system of claim 2 further comprising:

first and second ferro-magnetic stops,

said permanent magnet having first and second ends,

said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, a ferromagnetic core through said coil, said ferromagnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

5. A system for signaling the occurence of a predetermined event comprising:

a permanent magnet movable between a first position and a second position,

a coil magnetically coupled to said magnet, the flux of said magnet passing in a first direction through the core of said coil when said magnet is in said first position, the flux of said magnet passing in a second direction through the core of said coil when said magnet is in said second position, said second direction being substantially opposite from siad first direction,

snap action means responsive to said event to rapidly switch said magnet from said firest position to said second position in response to said event,

a radio frequency oscillator coupled to the output of said coil to provide a substantially unmodulated radio frequency output signal having a predetermined frequency in response to said switching of said magnet,

a super-regenerative receiver within signalling distance of said signal, said receiver being tuned to said predetermined frequency, said receiver having a normal noise output, said noise output being quenched by the receipt of said signal.

first relay energized by and held in an energized state by said normal noise output of said superregenerative receiver, and,

an alarm responsive to the state of said relay, said alarm producing an alarm signal in response to the switching of said relay from said energized state to an unenergized state.

6. The system of claim wherein:

said first relay has a first contact that is open when said first relay is unenergized and closed when said first relay is energized, by

said system further comprising:

a second relay having a holding circuit that includes said first contact of said first relay, said first contact when opened breaking the holding circuit and deenergizing said second relay, said second relay having a second contact that is open when said second relay is energized and closed when said second relay is de-energized,

said alarm being connected to a source of power through said second contact of said second relay.

7. The system of claim 5 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends,

8. The system of claim 6 further comprising:

first and second ferro-magnetic stops,

said permanent magnet having first and second ends,

and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferromagnetic path external to said magnet between the 5 ends of said magnet when said magnet is in said first position and when in said second position.

9. In a system for signalling the occurrence of a predetermined event, the transmitter comprising:

a coil a permanent magnet positioned with its flux coupled to said coil,

said flux of said magnet being coupled to said coil in a first direction through the core of said coil when said magnet is in said first position,

said flux of said magnet being coupled to said coil in a second direction through the core of said coil when said magnet is in said second position, said second direction being substantially opposite from said first direction,

a radio frequency oscillator circuit energized solely by said output pulse to provide a substantially unmodulated radio frequency output signal having a predetermined frequency and a duration substantially determined by said pulse.

10. The transmitter of claim 9 further comprising:

first and second ferro-magnetic stops,

said permanent magnet having first and second ends,

and a ferromagnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferromagnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

11. In an alarm system for producing a pulse of a substantially unmodulated radio frequency signal having a predetermined frequency and generated in response to the occurrence of a predetermined event, the receiving unit comprising:

a super-regenerative receiver within signalling distance of said signal, said receiver being tuned to said predetermined frequency, said receiver having a normal noise output, said noise output being quenched by the receipt of said signal,

a first relay energized by and held in an energized state by said normal noise output of said superregenerative receiver, and,

12. The receiving unit of claim 11 wherein:

said unit further comprising:

9 10 a second relay having a holding circuit that includes relay is energized and closed when said second said first contact of said first relay, said first contact relay is cle-energized, when opened breaking the holding circuit and desaid alarm being connected to a source of power energizing said second relay, said second relay havthrough said second contact of said second relay.

ing a second contact that is open when said second 5

Claims

1. An alarm system comprising: a coil a permanent magnet positioned with its flux coupled to said coil, said magnet being mounted for snap action movement between a first position and a second position, said flux of said magnet being coupled to said coil in a first direction when said magnet is in said first position, said flux of said magnet being coupled to said coil in a second direction when said magnet is in said second position, said second direction being substantially opposite from said first direction, said snap action movement of said magnet inducing an output pulse from said coil, a radio frequency oscillator circuit energized solely by said pulse to provide a substantially unmodulated radio frequency output signal having a predetermined frequency and a duration substantially determined by said pulse, a super-regenerative receiver within radio transmitting distance of said radio frequency signal, said super-regenerative receiver being tuned to said predetermined frequency, said receiver being quenched by said signal, and relay means coupled to the output of said receiver and responsive to the state of said receiver to switch from a first state to a second state when said receiver is quenched for more than a predetermined time period, said duration of said pulse being greater than said predetermined time period.

2. The system of claim 1 wherein said relay means comprises: a first relay having a first contact that is open when said first relay in unenergized and closed when said first relay is energized, said first relay being energized by said output of said super-regenerative receiver, a second relay having a holding circuit that includes said first contact of said first relay, said first contact when opened breaking the holding circuit and de-energizing said second relay, said second relay having a second contact that is open when said second relay is energized and closed when said second relay is de-energized, alarm means connected to a source of power through said second contact of said second relay.

3. The system of claim 1 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends, said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop, said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

4. The system of claim 2 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends, said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop, said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

5. A system for signaling the occurence of a predetermined event comprising: a permanent magnet movable between a first position and a second position, a coil magnetically coupled to said magnet, the flux of said magnet passing in a first direction through the core of said coil when said magnet is in said first position, the flux of said magnet passing in a second direction through the core of said coil when said magnet is in said second position, said second direction being substantially opposite from siad first direction, snap action means responsive to said event to rapidly switch said magnet from said firest position to said second position in response to said event, a radio frequency oscillator coupled to the output of said coil to provide a substantially unmodulated radio frequency output signal having a predetermined frequency in response to said switching of said magnet, a super-regenerative receiver within signalling distance of said signal, said receiver being tuned to said predetermined frequency, said receiver having a normal noise output, said noise output being quenched by the receipt of said signal. a first relay energized by and held in an energized state by said normal noise output of said super-regenerative receiver, and, an alarm responsive to the state of said relay, said alarm producing an alarm signal in response to the switching of said relay from said energized state to an unenergized state.

6. The system of claim 5 wherein: said first relay has a first contact that is open when said first relay is unenergized and closed when said first relay is energized, by said system further comprising: a second relay having a holding circuit that includes said first contact of said first relay, said first contact when opened breaking the holding circuit and de-energizing said second relay, said second relay having a second contact that is open when said second relay is energized and closed when said second relay is de-energized, said alarm being connected to a source of power through said second contact of said second relay.

7. The system of claim 5 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends, said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop, said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said Magnet when said magnet is in said first position and when in said second position.

8. The system of claim 6 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends, said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop, said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

9. In a system for signalling the occurrence of a predetermined event, the transmitter comprising: a coil a permanent magnet positioned with its flux coupled to said coil, said magnet being mounted for snap action movement between a first position and a second position, said flux of said magnet being coupled to said coil in a first direction through the core of said coil when said magnet is in said first position, said flux of said magnet being coupled to said coil in a second direction through the core of said coil when said magnet is in said second position, said second direction being substantially opposite from said first direction, said snap action movement of said magnet inducing an output pulse from said coil, a radio frequency oscillator circuit energized solely by said output pulse to provide a substantially unmodulated radio frequency output signal having a predetermined frequency and a duration substantially determined by said pulse.

10. The transmitter of claim 9 further comprising: first and second ferro-magnetic stops, said permanent magnet having first and second ends, said magnet when in said first position having said first end in contact with said first stop and said second end in contact with said second stop, said magnet when in said second position having said first end in contact with said second stop and said second end in contact with said first stop, and a ferro-magnetic core through said coil, said ferro-magnetic ends and said ferro-magnetic core being connected to provide a continuous ferro-magnetic path external to said magnet between the ends of said magnet when said magnet is in said first position and when in said second position.

11. In an alarm system for producing a pulse of a substantially unmodulated radio frequency signal having a predetermined frequency and generated in response to the occurrence of a predetermined event, the receiving unit comprising: a super-regenerative receiver within signalling distance of said signal, said receiver being tuned to said predetermined frequency, said receiver having a normal noise output, said noise output being quenched by the receipt of said signal, a first relay energized by and held in an energized state by said normal noise output of said super-regenerative receiver, and, an alarm responsive to the state of said relay, said alarm producing an alarm signal in response to the switching of said relay from said energized state to an unenergized state.

12. The receiving unit of claim 11 wherein: said first relay has a first contact that is open when said first relay is unenergized and closed when said first relay is energized, by said unit further comprising: a second relay having a holding circuit that includes said first contact of said first relay, said first contact when opened breaking the holding circuit and de-energizing said second relay, said second relay having a second contact that is open when said second relay is energized and closed when said second relay is de-energized, said alarm being connected to a source of power through said second contact of said second Relay.