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I'm in the process of installing an alarm system that supports 2 or 4 wire low voltage fire alarms.

The house is wired with high voltage single wire smoke alarms.

As I understand it, there are relays that can wire into the circuit and either act as the sender or receiver for low or high voltage accessory devices like pull switches or lighting. An example device is referenced here.

As I also understand it, these relays cannot be used to wire into alarm panels.

So my question: What is the reasoning behind not allowing this? Is it just because multi-wire detectors support zoning, or is it actually dangerous to do this?

Are there devices that exist that do allow me to do this, or do I need to switch detectors?

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Such connections are not UL, CSA, or NFPA rated because the alarm panel cannot supervise the smoke alarm circuit. 2 and 4 wire low voltage alarm circuit are supervised and report more to the alarm panel than simply an alarm condition. For example, if properly wired, damaged wiring or missing detectors will cause a trouble condition.

You can physically do what your wondering (use the relay between 120v smoke alarms and an alarm panel). Only an alarm condition can be detected (not low battery as the 120v detectors have).

In a previous version of this answer I didn't say it the best, but as @gregmac points out in a comment, if you do this for your own benefit fine. Don't ask your insurance company for the discount given for a listed monitored fire protection system, because this is not an approved method.

The smoke detector manufacturers such as Firex and BRK do make such relays available to activate other devices such as strobes or exit lighting (not to be confused with an "EXIT" light in a commercial or multi-family building), but not for means of UL or CSA rated alarm reporting.

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    I think what matters is if your insurance requires this -- eg, you are getting a premium discount because you have a monitored fire alarm system. I have fire insurance on my house even though I don't have an alarm system (just regular smoke detectors) -- but my insurance company knows I don't. I don't see why you can't use the relay method to connect your smoke detectors to the alarm system, so long as you don't claim to have a monitored fire alarm (in other words: "we'll pay if your house burns down if you don't have a monitored alarm, but we won't if you do and it doesn't work"?) – gregmac Jan 12 '17 at 21:26
  • I appreciate the clarification. In my particular case this seems to solve the short term problem of being personally alerted if there's a problem as I transition them into 2/4 wire sensors in the long term. – Steve Jan 13 '17 at 15:03

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