A system and method for monitoring whether a resident is away from home or inactive within the home. A sensor, which includes a transmitter, a processor, a timer, and a detector, watches for motion to occur within a home. Upon sensing motion, the sensor sends a first signal indicative of the motion if the timer is not currently running and waits for the motion to end. If the timer already is running, the timer is restarted at zero. Upon expiration of a predetermined timing period, the sensor transmits a second signal indicative of inactivity. By comparing the timing of the second signal and the predetermined timing period, with a third signal sent by an exterior door sensor, a determination can be made whether the resident has left the home or is inactive within the home. The system includes a database, a CPU and State Model for determining the activity state of a home.