SPY3931 is a Stanley Vibration Activated Alarm, which is an ideal way to protect and secure your property. It is an easy-to-install, wireless alarm system that is triggered by vibration. It can be placed on a door or window to detect any movement. The alarm emits a loud, ear-piercing sound when activated, making it an excellent deterrent for unwelcomed visitors. The alarm is powered by a 9V battery, which is included in the package. It is also weatherproof and will provide protection even in harsh environmental conditions.