A key input device comprises a dome sheet 7 provided over a base plate 5 and having a plurality of dome portions, and a plurality of manual keys disposed above the dome sheet 7 for depressing the respective dome portions. Each of the dome portions is elastically restorably inverted by being depressed...http://www.google.co.uk/patents/US6633641?utm_source=gb-gplus-sharePatent US6633641 - Key input device
