The Motion sensor requires (2) - 'AA' Lithium batteries. You can purchase these batteries at stores like Walmart, Superstore and Best Buy. Liberty recommends using one of the following:
*Note: Before changing the Batteries on any of your devices, contact Liberty at 1-866-926-7233 so that your system can be put on 'Test mode' to avoid getting a tamper alert or call from the monitoring station.
For a demonstration on how to replace the batteries please watch the following video: