TX-E201—Battery Replacement
The TX-E201 door/window sensor requires a CR2032 3-volt lithium battery, which can be purchased at your local hardware, mass retailer, or battery store.
You may also order these online here or at your preferred online retailer.
Interlogix TX-E201 / Ecolink WST-201 Mini Door Window Sensor:
In order to replace the CR2032 3V lithium battery for replacement, slide down the back cover to remove it as shown below.