Our electrician went to a customer's home who requested to have 2 smoke detectors replaced with a hard wired versions. The wiring is installed, but battery units were used in the past. He replaced the smoke detector on the first floor and the detector on 2nd floor. He also found extra wiring in the 2nd floor box indicating a 3rd smoke detector located elsewhere in the home. He showed the location to the homeowner and added a charge to replace the 3rd unit as well. He tested the operation to verify the interconnect works and waited to make sure they would not chirp or have other communication problems.
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