In Kentucky we have really weird laws concerning smoke detectors so we run into this a lot. We use the FF433 and the 2Gig equivalent on occasion. One advantage it has over the Kidde relay is it still works in a power outage. The Kidde is a good piece if you read all the fine print in the manual. We had issues with false alarms so we stopped using them. Another option is the GE 350CX. We'll either sell them to the electrician, or go in after and swap the electrician's out. They also have a model that will let you set up every smoke as a separate zone.