Monitor doors, windows, gun cases, jewelry boxes, or just about anything that opens and closes. The Wireless Magnetic Door / Window Contact Sensor is a protective device that can send notification when the opening and closure of doors and windows occurs. It is designed to send a wireless signal to a compatible home security system when the contact between the transmitter and corresponding magnetic sensor is broken. Additionally, an LED light illuminates whenever the magnetic contact is broken. An Anti-collision algorithm prevents signal jamming by simultaneous transmission from multiple devices. This wireless sensor is powered by a 3.6 V Lithium CR-2-type battery, included, that typically lasts about three years. A weak battery will transmit a message during any status report the system completes. This protective device is typically used on entry points, such as doors and windows, that are normally closed. Each magnetic contact also features a connection for a hardwired sensor input, making it ideal for protecting multiple windows using standard contacts and only one wireless version. Enabled with a unique ID code, each magnetic door and window contact is available in several optional frequencies in compliance with international standards.