Abstract: An intrusion alarm system utilizes an inertially responsive sensor preferably present as a pendulum actuated reed switch. Logic circuits provided within the system provide, an efficient pulsating alarm at dual frequencies optimized for human recognition. In both arrangements, a unique dual delay arrangement is provided, one delay commencing with the arming of the device to permit adequate time for the setting of a sensing switch. A second delay arrangement is provided at the option of the operator for purposes of delaying the activation of the alarm once the sensor switch has been tripped. This feature may be utilized to permit entrance through a door or the like upon which the unit is mounted wherein the device can be deactivated prior to assuming an alarm sounding condition.