Programmed security alarm system - with suitable binary code combination that must agree with one entered via push button inputs

摘要

A security alarm system allows a coded combination to be pre-programmed that has to be entered into the unit for comparison before entry is allowed into a restricted area. The alarm system is encased in a single module (14) with apertures (16, 18) for emitting an acoustic alarm signal. A programming push-button (20) is coupled over a switching stage to a plunger to a ratchet wheel. The buttonis successively operated to move the ratchet to index cams to a selected binary code. Typically a four bit code is used and this is compared with one entered using four buttons (24, 25, 26, 27) on the front panel. The entered code is displayed (29-32) on the front panel. When the two code combinations agree entry is allowed.