2-n-1 Door Knob Alarm
This Door Knob Alarm can be used as a burglar and personal alarm. You can put it on any type of door knob on a non-metallic door and it automatically and instantly will sound anytime the door knob’s touched by an intruder. You can also take it with you and pull out the chain to sound its 120-decibel alarm. It takes a single 9-volt battery.
Requires one 9 volt battery, not included. Dimensions: 4 ¼" x 2 ¼" x 1"