Abstract: An activation and deactivation circuit is provided for a security alarm system and includes selector means for selecting a predetermined coded number for enabling and disabling the alarm system. A coded circuit is responsive to the predetermined code from the selector to produce a control signal for enabling the alarm circuit when disabled and disabling the alarm circuit when enabled. Should an error in the predetermined coded number be detected, it is registered in a memory circuit and a second error will activate the alarm, thereby indicating tampering by unauthorized personnel.