Situation I have is building with Tavern & apartment 1st floor. Second floor 2 apartments, front and back. Remodeling (gutty out) upper front apt, complete rewire with subpanel in apartment. Apt had OLD smoke det. from the 80's (System Sensor) low voltage (12V). Old system has units in each apt and tavern, one goes off, they all do. O.K. Problem System Sensor no longer makes of sells that model, according to their Tech. He gave me other model #'s that might work with the old system. Tech said to search Ebay, did that nothing on Ebay that would work. Tech recommends all new system. The Owner of building says Bull Hockey!! I explained the problem and gave him an 8 pages of tech info of the old system. He says just put "battery operated smoke in remodel unit". I say they have to be "interconnected". I said, could install a Kidde wireless smoke detectors with the base hardwired unit, around $500. I want to contact Building Inspector, around here he determines where and what is used in buildings. Owner says NO, doesn't want inspector called. I say I am off the job, unless some kind of interconnected system is installed. Owner says that interconnect is ONLY for 4 unit apartment buildings. BULL. Owner said he will sign any papers I want him to. Now I should get legal papers drawn up for that, so when someone gets killed in fire, those papers are going to stand up in Court. You Bet!! Need your opinion Guys & Gals. Thank You for your time and opinion. Mick