Abstract: A permutation lock having pushbutton code controls and automatic cancelling of the code when the latch is operated for opening the door. An adjustable time-delay device is provided for disabling the operation of the lock after a predetermined time from when the code is inserted in the lock chamber. The time delay device disables the lock after the duration of a predetermined time.

Abstract: A back-up safety system stops the engine of a machine such as a power mower upon failure of a main safety system whereby release of a dead man control normally declutches a work performing member from the engine and brakes it to a stop while the engine continues to run. The back-up safety system comprises a switch that is closed upon release of the dead man control, in series with an SCR in a magneto grounding circuit. The SCR is gated on by a sensor comprising a biasing coil connected with the SCR, a ferromagnetic rotor constrained to rotate with the work performing member and having circumferentially spaced pole projections, a permanent magnet, and a core with which the coil is coupled and which cooperates with the rotor and magnet to define a magnetic circuit wherein flux density varies as rotor projections pass a pole face on the core.