Antitheft alarm system for household security - has initial intermediate trigger stage activated by movement or e.g. window and uses bistable multivibrator coupled to XOR-gate

摘要

The security system has a detector associated with at least one access door or window for operating an alarm via intermediate release stages. An initial intermediate stage (2) is activated by the door or window being closed and controls a logic circuit (6) supplying a signal which causes the initial stage (2) to be responsive to a successive operation of the door or window. The initial intermediate stage (2) uses a bistable multivibrator (4), with one input coupled to the output of an EXCLUSIVE OR gate (5) in turn coupled to the detector (1). The other input of this gate is coupled to the logic circuit (6) while a delay stage is coupled between the intermediate stage and the logic circuit.