Replacing a room sensor battery involves gently prying off the battery cover, popping the battery out, and replacing it with a fresh CR2032 coin cell battery, inserted positive side up.
ecobee room sensors use 3 Volt CR-2032 batteries that are readily available in most hardware stores.
If your sensor is using a sensor stand:
1) Place your thumb and index finger on the narrow part of the sensor stand, and your other hand on the front of the sensor
2) Gently pull the upwards to remove it from the stand
3) Remove the battery by gently prying it out of the battery compartment with a thin tool such as a pen, plastic card, or screwdriver
If your sensor is using the circular battery cover:
1) Using a thin tool such as a pen, plastic card, or screwdriver, slip the tool into one of the recessed corners of the battery cover
2) Gently pry the battery cover off
3) Using the same tool, gently pry the battery from the battery compartment
Inserting a new battery:
Ensure the battery is inserted positive (+) side up as shown here. You will need to push the battery gently to allow the metal prongs to hold the battery into place.