To replace the battery:
Slide the top cover to disengage (unlock) it from the sensor, then remove it to reveal the battery.
Replace with a CR2032 battery ensuring the + side of the battery faces towards you.
Re-attached the cover, ensure the Top (as marked on the inside of the cover) points away from the battery. Slide the cover toward the sensor to engage (lock) it, you should hear a click when the cover engages properly.
