An electrically wired doorbell requires a transformer to step down the 120-volt house circuit to the correct voltage and wattage required by your doorbell. A doorbell transformer is a small brass or silver colored box about 2 to 3 inches square with two to three terminal screws on the face. You may need to replace the transformer if it has failed or if you are installing a new doorbell. First, you must find the original transformer installation location.
Check behind your existing doorbell. Remove the doorbell from the wall to see if the original installer placed the transformer in an electrical box directly behind the doorbell.
Look inside your coat closet if it is near your front door or the doorbell. Look above the closet door and on the front wall.
Turn off your main breaker at the service panel and remove the cover. Some installers will place the transformer at the bottom of the service panel.
Look around your garage above your service panel if it is in the garage. Look on the wall of the garage nearest to your front door. The transformer will be near the ceiling to avoid tampering.
Check inside your furnace closet. Look above the door and along the walls for the doorbell transformer.
Gain access to your attic or basement. Look near the front door location or directly above or beneath the doorbell location. Check beneath the stairs in the basement for the hiding place of the transformer.
Look beneath your stairwell in a two-story house if you have a storage area under the stairs. Some installers place the transformers in areas that are not often disturbed.