U.S. Patrol JB5533 Watchdog Door Knob Alarm
Scare off unwanted intruders. Inexpensive way to keep your home safe and secure. Requires NO special wiring. Simply hang on the inside door knob. System works even if the intruder comes within inches of the knob. Ideal for any door knob...at home, office, dorm, hotel room...anywhere. Takes 1 - 9 volt battery.