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 door knob. The 2-in-1 Alarm is great protection against unwanted visitors. Requires one 9 Volt battery. What you should know about our NEW Door Alarm: Can also be used as a personal alarm.  Simply pull the attached pin. Be prepared, scare muggers away!!! Door alarm - simply install 1 9 Volt battery and hang on the inside door knob. Alarm will also work if intruder is wearing GLOVES as this alarm will detect the body electricity. CAUTION:  Extremely loud.