Smoke Detector Wiring for Your Home

The 2-Wire System - Older Homes

Many homes still only have one 2-wire smoke detector usually found in the hallway leading to the bedrooms or a stairwell.
Adding additional smoke detectors in other required areas such as individual bedrooms while converting the original smoke detector is relatively easy, as shown in the installation photos shown below.
A typical construction project will require a smoke detector in each bedroom and on the ceiling or wall at a point centrally located in the area giving access to bedrooms such as hallways.

The wires are stripped and ready to make up. Notice that the ground wire is attached to the ground screw provided in the junction box. After the mounting adapter is screwed to the cut in box the wire plug which came with the smoke detector is attached using wire nuts. With the smoke detector plugged in the smoke detector is attached to the mounting adapter.

Back at the existing smoke detector junction box the new wires are ready to be attached to the existing wires, blacks to blacks, whites to whites and the grounds bonded to each other and to the metal junction box. The new red wire of the 3-wire romex is attached to the smoke detector's yellow wire and is used to send the alarm signal between all the smoke detectors that will be installed. The adapter plate and plug are ready fro the new smoke detector which takes the place of the old smoke detector which did not have the third wire capability to interconnect all the smoke detectors together

The power is turned back on and the green power indicator LED lights up. To smoke detector is tested by pressing the test button until the alarm sounds. The alarm usually sounds once then sends the signal to the other smoke detectors causing them to all go into alarm for a short test period.