Securing your home, apartment or small business has never been easier or more affordable. Simply install the Mace Brand Digital Door & Window Alarm on any door or window, and when the door or window is opened, the alarm will sound. Installation is quick and easy. Any entry to a protected door or window will activate the 100 dB siren for 30 seconds. The alarm automatically resets and continues sounding until the door or window is closed or the alarm is disarmed. Window or door coverage may be expanded by purchasing additional magnetic sensors, item #80374. The device is suitable for indoor use only. Requires three LR44 batteries, included.