When it is time to replace the battery in your motion detector, you will see an alert on your system panel.
The TX-E721 motion detector requires a CR123A 3-volt lithium battery, which can be purchased from Indiana Alarm, local hardware store, mass retailer, or battery store.
1. Locate the sensor with a low battery on your system panel.
2. Open the cover by pressing the tab at the bottom of the sensor.
3. Remove and replace the CR123A 3-volt lithium battery.
4. Make sure the area where the batteries are stored is clean and there is no corrosion.
5. Put the cover back on starting with the opposite end from which it was opened. You should hear a snapping sound if it closes correctly.
7. Check if the low battery status has cleared