# Device to detect when power is not present
**URL:** https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024
**Category:** Devices
**Created:** [March 18, 2025, 9:51pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024 "2025-03-18T21:51:10Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Carl\_Proescholdt](https://community.homey.app/u/Carl_Proescholdt)
#### Post date: [March 18, 2025, 9:51pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/1 "2025-03-18T21:51:10Z")
On the surface, this seems like it should be easy, but I am having a mind block on how this can, or should be done in a simple fashion. I would like to monitor if power is present to a 240 volt appliance. In this case, our HVAC system. I would like to be able to take action on, or notify me, when the power goes off on our heating/air conditioning system. Anything I can think of doesn’t work once the power is interrupted. I am open to ideas on what devices, or approaches would be ideal for this. Thanks.
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### Author:  [@Andy\_Henderson](https://community.homey.app/u/Andy_Henderson)
#### Post date: [March 18, 2025, 11:26pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/2 "2025-03-18T23:26:40Z")
One possibility is to run a low-wattage light off the same supply and use a battery-powered light sensor to detect and report when the light goes out. If you put both in an opaque box that would increase reliability.
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### Author:  [@Jonathan\_Draper](https://community.homey.app/u/Jonathan_Draper)
#### Post date: [March 19, 2025, 3:19pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/3 "2025-03-19T15:19:03Z")
If the interruption to power does not also affect your Homey then connecting the HVAC via a power metering device would allow Homey to notify you if the HVAC was no longer consuming any power.
If the power to Homey itself is maybe interrupted then you can enable Offline warning setting under Settings \> General in the Homey app to get notified when your Homey is no longer connected to the Athom cloud. Of course that could also be your Internet going down but that would likely prevent any other method working also.
Either of those any good?
EDIT: Or if you’re worried about the whole circuit the HVAC is on losing power then connect the HVAC via a Shelly Wifi device then use the [Net Scan App for Homey | Homey](https://homey.app/en-gb/app/com.netscan/Net-Scan/) to detect when the Shelly device leaves your network. If you use a Shelly device with power metering you can combine this with the first option above for issues where the circuit is fine but the HVAC itself fails
EDIT: I just tested the approach using Netscan and a Shelly relay device and it works a charm. Within about 30s of switching off the power to the relevant circuit I got a notification from my flow on Homey using a trigger from the Netscan app.
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### Author:  [@Carl\_Proescholdt](https://community.homey.app/u/Carl_Proescholdt)
#### Post date: [March 19, 2025, 7:34pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/4 "2025-03-19T19:34:56Z")
Andy,
Interesting approach! That would electrically isolate the monitoring from the power feed of being monitored. I will keep that idea in my hip pocket.
Carl
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### Author:  [@Carl\_Proescholdt](https://community.homey.app/u/Carl_Proescholdt)
#### Post date: [March 19, 2025, 7:38pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/5 "2025-03-19T19:38:23Z")
Jonathan,
A power monitoring device is just the ticket I think. I can supply the power to it separately so it stays alive. Specifically, which Shelly device are you thinking about. (I am on a US power system).
I haven’t used the Net Scan App. That offers an interesting twist. I will also look into that.
Thanks.
Carl
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### Author:  [@Jonathan\_Draper](https://community.homey.app/u/Jonathan_Draper)
#### Post date: [March 19, 2025, 9:44pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/6 "2025-03-19T21:44:19Z")
Something like this should have you covered. You’d need to connect the HVAC to the switched output to have it power monitored but you can just use it for power monitoring if you don’t need to switch it.
> **[Shelly 1PM Gen3](https://us.shelly.com/products/shelly-1pm-gen3)**
>
> Shelly provides advanced smart home automation solutions for seamless control of lighting, temperature, and energy. Make your home smarter today.
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### Author:  [@Carl\_Proescholdt](https://community.homey.app/u/Carl_Proescholdt)
#### Post date: [March 20, 2025, 4:27pm UTC](https://community.homey.app/t/device-to-detect-when-power-is-not-present/133024/7 "2025-03-20T16:27:57Z")
Thanks Jonathan! I’m going to give this a go. In the meantime, I already put NetScan to work on other applications. Appreciate the tips!
Carl