AC usage device - exists?

What I’m seeking is a device that, when you turn on an AC circuit, tells Smartthings “I’m on”. It does not have to report OFF status; I can have the ST app manage that.

The idea is to ‘accessorize’ a bathroom ceiling fan. I don’t want a smart fan that is controllable from ST. I just want ST to know when that fan has been turned on. So hypothetically the device could sit inline between the fan and the wall switch (no neutral, unfortunately).

Turning on the fan will then trigger a different thing elsewhere in the system. (For those who might be curious, it will be telling the audio system to turn up the speaker in the bathroom to a volume that can be heard over that fan!)

Zigbee or Zwave, as I do not have Matter set up.

Would a smart rocker switch do this? Or does it require the neutral for all smart functionality?

A smart switch would do this as well as let you control the fan. If you go that way you need to find a switch (not a dimmer) that is specifically meant for fans. Fans have a higher current requirement and especially a high initial inrush current so a switch meant for a light bulb isn’t safe.

I’m not sure if there are any which work without a neutral. Neutral wires in junction boxes for switches are relatively new addition to US electrical code. They are necessary to provide always-on power for the smart device itself, separate from what the smart device is controlling.

I don’t know how this would work but I did turn up a current sensor that works via z-wave with SmartThings. No clue how this would present itself in the ST app, though.

Aeotec by Aeon Labs ZW095 ZW095-A Home Energy Meter Gen5 Zwave Power Monitor Small White

@JDRoberts encyclopedic knowledge will probably help here!

I don’t know of any smart switches that can handle a fan motor that don’t require a neutral. Certainly none that are UL listed. :thinking:

As far as inline devices monitoring current draw, sure, there are lots of devices to do that. Again, you need to make sure that it matches the motor specs, but it should certainly be doable. Shelly plus 1 PM should be a good candidate, I think it reports the power usage to SmartThings in an actionable way, but verify that before purchasing. I know the Shelly Smart plug does.

If you use the official integration, it will be cloud cloud, but there’s also a community edge driver, which can give you local integration if that’s what you want, as long as you have a SmartThings/aeotec hub

Edge Shelly drivers for Gen1 and Gen2 Devices

The Aeotec HEM that was already mentioned is another possibility, but it goes at the circuit box, and measures the entire circuit, which didn’t sound like what you wanted. Also, it’s much more expensive: simple relays with energy monitoring like the Shelly should be under $30.

As always, it would help to know the brand and model of the ceiling fan so we know what the draw is. :thinking:

I got the impression it was a bathroom extractor fan. I wouldn’t expect a ceiling fan to generate enough noise that the speaker volume would need to be raised. :sunglasses:

Yeah, the op said:

bathroom ceiling fan

Extractor fans are also called ceiling fans since they are typically installed in the ceiling. I was just trying to match the OP terminology since it didn’t really matter in this case.

Knowing the brand/model would still let us know the HP of the motor, which is the important thing for matching specs to the monitoring device. :sunglasses:

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Bathroom exhaust fan perhaps? Bathroom vent fan?

Will see if I can find the brand/model.

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I have used the SmartThings multipurpose sensor for various purposes, triggering automations based on vibration for my old generator, septic alarm, etc. You might consider attaching one of these sensors to the fan to trigger the fan’s ‘on’ state instead of relying on power.

Works really well with Zigbee Contact MC

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I tried that already. I’m using the multisensor on my dryer vent tube to trigger Alexa announcements, and on my bathroom door to trigger lights on. The fan does not vibrate enough to activate the sensor (side note: I tried it on a skylight some years ago, and despite the combo of movement and vibration that also could not activate it). So the sensor, despite being very useful in many scenarios, has limitations.


I think I figured out an answer. While the switch leg does not contain a neutral, the power wire to the fan certainly does. So a neutral-powered smart relay can be mounted in the ceiling, next to the fan.