Batteries in Honeywell's wireless window and door sensors generally last 5 to 7 years. The battery life can vary depending on the frequency with which the door or window is opened and closed. Before the battery completely dies, the wireless window and door sensor will send a low battery signal to your Honeywell wireless alarm control panel along with the (2) digit zone number so you know which device needs service. You have approximately (30) days to replace the battery in the affected wireless sensor before it will stop working. However, you should replace the battery sooner than later as the wireless window or door sensor may not work optimally with a battery that is low.