Line voltage smoke detectors for residential are interconnected with 14-3 wire and if one sounds they all will go into alarm.I use BRK and use photo electric type within 20 feet of a bathroom or kitchen and ionization elsewhere.We use the type with battery backup.
Put 1 on each level near stairwell and add a 2nd if the floor area is over 1200sq feet. Also put 1 in each bedroom. I put heat detectors in the garage and also in an attic with mechanical equipment.Keep 3 feet away from ventilation duct feed and returns.
Connect to a AFCI circuit according to 2002 NEC.
Do not use more than 12 smoke detectors interconnected.
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