This door alarm installs in seconds, without any special wiring, on any non-metallic door. It will sound an instant ear piercing alarm if anyone touches your doorknob.The 2-in-1 Alarm is great protection against unwanted visitors. Requires one 9 Volt battery (NOT INCLUDED)It acts as a burglar alarm and a personal alarm. Hang it on any door know (non-metallic door) and it instantly and automatically sounds when an intruder touches the door knob.Carry it with you and just pull out the metal chain to sound the alarm and deter an assailant.The alarm is 120 decibels. Requires one 9 volt battery (NOT INCLUDED)ITEM # AL-2