Seat belt warning device

Claim 1

A warning device for a seat belt having connectable buckle and key, the device comprising an electronic unit carried by the buckle of the seat belt, and a magnetically-operated switch incorporated in said unit actuation of which causes a warning signal to be transmitted by said electronic unit, the arrangement being such that, on insertion of the key of the seat belt into the buckle, the switch is actuated whereby a signal indicative of connection of the seat belt is transmitted by the electronic unit, and, on removal of the key from the buckle, the switch is actuated whereby a signal indicative of disconnection of the seat belt is transmitted by the electronic unit, said electronic unit comprising a bistable circuit incorporating said magnetically-operated switch, and a magnet movable with a sensing element, the arrangement being such that, on movement of the sensing element from an inoperative position to an operative position, the magnet is moved away from the switch to open said switch and actuate the bistable circuit whereby the signal indicative of connection is transmitted, and, on return of the sensing element to its inoperative position, the magnet is moved towards the switch to close said switch and actuate the bistable circuit whereby the signal indicative of disconnection is transmitted, said bistable circuit further including an audible device which is actuated on opening and closing of the switch, the output from the circuit on opening of the switch being of short duration, and the output from the circuit on closing of the switch being of longer duration.