Battery Tutorial: Recessed Door Sensor (DW21)
You will need one CR2 battery and a coin such as a penny to change the battery in your door sensor. Before changing the battery, make sure that your system is disarmed and note that you may here some beeping from the panel when you open the sensor. Go to your door sensor and use the coin to twist the sensor out of the door. Remove the old battery and replace it with the new CR2 battery. Slide the sensor back into the door frame with the two guides lined up. Use your coin to twist the sensor to the right to tighten it into place. Remember to safely dispose of the old battery. For more information and tutorials, please visit support.vivint.com.