Mini Door & Window Contact Alarm & Chime Set of 4 Inconspicuous: Only 2.5" long. Easily mounted by adhesive tape to window or door, no tools required. 4 alarms per pack. Loud 90 dB alarm scare off potential intruders - Magnetic sensor switch detects entry protecting you home or office whether you're in or out. Chime or alarm mode. Residential use: Protects exterior door, sliding glass door, gun and medicine cabinets Commercial use: Protects showcases and cash registers Operated by three 1.5VLR44 button cell batteries