This Glass Break Sensor takes 1 CR123A battery and the typical battery life for the sensor is 3-5 years.
1.
Open the Glass Break Sensor by unscrewing the Philips head screw on the bottom of the Sensor.
2.
Replace the CR123A battery. Make sure to follow the polarity requirement.
3.
Once the new batteries are placed, place the front cover back on the face of the sensor and tighten the screw back in.