Magnetic door/window alarm with included batteries is only 2-1/2" long to discreetly protect your home or office from intruders. Magnetic sensor detects when opened to quickly signal when a break-in occurs. 110-decibel alarm delivers a loud alert signal to notify you and scare off potential intruders. Versatile construction can also be used on medicine cabinets, sliding doors, showcases, cash registers and more. Included double-sided adhesive tape makes installation fast and simple..