Designed to sense open windows or doors. Both components have double sided adhesive tape for easy installation. Generates a loud, piercing alarm when the units are separated by 1/2". Alarm has on/off switch. Operates on three LR44 button batteries (included). This very interesting, inexpensive and clever alarm can be adapted to other proximity sensing applications. Blister packed for retail sales. Imported for ongoing availability. ME059 - 1 in stock