A table-saw having dual guards, one being that for the saw to run the guard must always be in correct vertical and horizontal operating position covering the whirling saw blade, and the other being that the saw is automatically shut off after a waiting period in the event that the operator is not actually...http://www.google.co.uk/patents/US4033218?utm_source=gb-gplus-sharePatent US4033218 - Table-saw guard
