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  • What is the signalling voltage on hardwire smoke detectors?
  • Is it acceptable to mix brands?
  • Is it acceptable to have detectors on different electrical circuits, connected only with an interconnect wire (will that cause the interconnect to be referenced to the wrong ground level?).

Why? I have an existing hardwire OneLink alarm, and a battery powered slave. But the corresponding hardwire BRK alarms get terrible reviews (see Passive-Aggressive smoke detectors for the type of problem). I'd like to know if I can purchase higher quality units and still interconnect them.

The OneLink alarms transmit extra digital data wirelessly (e.g. the room and alarm type)... do they do that over the interconnect wire also?

The vendor instructions of course tell you to use only matching alarms.

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All hardwired alarms are interoperable. If one alarm goes off it energizes the third wire and all other ones go screaming too. I have quite a few hardwired alarms and many of them are different brands.

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I've read elsewhere of problems with interchangeability, even within the same brand. What's the type of signal sent on the interconnect wire? – Bryce Aug 14 '12 at 23:00
I always thought the third wire just uses simple on/off signal. Probably 9v, since that's the backup battery voltage on the smoke alarm. Now I'm not so sure :) however empirical evidence from bunch of different alarms going off at once suggests that they operate just fine. – Vitaliy Aug 16 '12 at 21:09

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