These Philips Battery-Operated Window and Door Alarms provide a simple-to-use, cost-effective security solution to protect you and your family. Thanks to reliable magnetic sensors and 120-decibel alarms, a would-be intruder will think twice about entering your home. This set of four user-friendly alarms will provide you with the extra coverage you need. You can also choose between alarm or chime modes with the flip of a switch. When installed and armed, the alarm will activate if the window or door is opened, alerting you and deterring unwanted visitors. The simple, wire-free design of these alarms are perfect for homes, apartments, dorm rooms and offices alike. Use the included double-sided mounting tape to attach them to your window or door of choice within minutes — each alarm is powered by four LR44 button batteries (included).