Abstract

A security alarm system which may be selectively armed or disarmed when monitoring a protected premises is described which utilizes the position of a deadbolt to determine whether the security system should be armed or disarmed. The security system comprises (i) an entry door for permitting ingress to the protected premises from the outside of the entry door and egress from the protected premises from the inside of the entry door; (ii) a lock for selectively locking and unlocking the entry door; and (iii) a switch having a first state indicative of the lock being in a locked position and a second state indicative of the lock being in an unlocked position wherein, when the switch is in its first state, the security system is armed and, when the switch is in its second state, the security system is disarmed. Sensing means are also provided to determine if the lock was engaged from inside or outside the protected premises. In the case where the lock was engaged from outside the premises and no authorized individual remains inside, sensors inside the premises would become activated. Conversely, in the case where the lock was engaged from inside the premises or from outside the premises and an authorized individual remains inside, the inside sensors would remain deactivated. The disabling of an inadvertent (false) alarm is easily, yet securely, achieved by activating a first user-controlled disarming means and returning the lock to its unlocked position.