What's Required?

In most areas, smoke detector requirements and placement are covered in the building code. Check with your local jurisdiction to be sure you understand what the requirements are for your area. Once you know where to install them, the wiring method for them is the same everywhere.

Power

Smoke detectors need to be hard-wired into your house electrical system. You only need to power one of your smoke detectors from a regular power circuit, the rest will get their power from the cable that inter-connects them. For their power, use a general circuit, one that doesn't have restrictedrules on it. While it is legal, it's not a good idea to use a bedroom circuit, as this circuit will be on an AFCI. Pick a general use 15 amp circuit such as a hallway, living room, family room etc..

Connect them Together

Smoke detectors must all be connected together, so they all sound the alarm together. To accomplish this, you need to interconnect them with a 3-wire cable (14-3 if you have them on a 15 amp circuit). The black and white wires in the cable carry the main power for the detector, and the red wire will carry a signal to tell the detectors if one is in alarm.