The batteries on wireless sensors last about 5 years. The alarm panel checks in with the sensors every 30 – 90 minutes, depending on the sensor. If the battery starts getting low on a sensor it will alert you about 6 months before the battery is actually dead, so there will be plenty of time to get the battery swapped. Should a sensor die, the alarm panel performs a regular check in with the sensor. If the sensor is dead or broken, it will not respond to the alarm panel , which will then result in a trouble condition on the panel. Call us if a sensor trouble should appear and we will make sure your sensors are all in working order.