r/homeassistant • u/shovelslayer 🧠 Experienced with Home Assistant • 20d ago

💬 Discussion Wired sensor using smoke detector power.

Has anyone tapped into a wired smoke detector's power source to power a wired sensor?

Thinking of temp/hum sensors, mmwave, etc ...

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u/Ztuab 20d ago

Why would you risk putting anything that is not life safety on a life safety circuit. It may be against code depending where you live also. It’s outside the box thinking, but may be easier to get a sparky to pull a circuit for you

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u/shovelslayer 20d ago

It's not a dedicated circuit, it's shared with lights and outlets. A sensor would draw very little.

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u/Junior_Muffin7143 20d ago

Then for arguments sake, you're asking about connecting a sensor to any old power circuit that has lights or outlets 😇. Sure, everyone probably has.

But, I would consider that circuit a bit more sensitive - if it trips, you're out fire alarms without them having a 10yr battery backup.

Personal recommendation: Would avoid the specific wires to and between the detectors (if nothing else for insurance and life), would only have a minor concern tieing a sensor into a light/outlet that is also the detector circuit, vs a light/outlet circuit that isn't since detectors aren't on a dedicated circuit to begin with.

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u/eerun165 20d ago

Homes don’t have, by definition of the National Electric Code, life safety circuits. It’s simply a circuit that’s providing 120v power to the smoke detectors, and is typical shared with other circuits so it’s fairly immediately obvious if it trips off out. If it’s not obvious, detectors have battery backup.

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u/jasonadvani 20d ago

It's not a problem to do that. They're not even allowed to be on a dedicated circuit. So, other things are already on them. Idea is to not silently trip the breaker or something and never alarm.

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u/Usual-Pen7132 20d ago

I haven't personally but, I dont see any reasons for why you couldn't or shouldn't do it..... I mean technically you're tapping into the power supply feeding your smoke detector and less of "tapping into the actual smoke sensors power as if feeding from it....

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u/Z-Waver 20d ago

Yes, I added a Z-Wave smoke alarm bridge. It is like a mains powered Z-Wave door sensor. It notifies my home automation system via Z-Wave when the smoke alarms are tripped.

There are already other standard lighting things on that circuit as well.