A sensor to detect if a device is powered on?

Hey everyone. I’m looking for advice on a device to notify me if something is powered on via mains power. In short, I’m trying to use my Smartthings to alert me if my alarm is going off. I have my alarm set to switch on a plain-old-electrical-outlet when it is going off, which I currently have a siren plugged into.

I’ve done some searching and I’ve found a few possibilities, mostly involving the v1 version of the Smartthings motion sensor:

… but I don’t own one of these, and this isn’t quite what I’m looking for since this actually detects when the power goes off, not on. I’m sure I could modify the app script to make it to go the other way, but I thought I’d check and see if anyone had any other ideas.

I was thinking maybe I might be able to modify one of my battery powered Everspring Flood sensors, or perhaps a door & window sensor with external contact plugs, to do the job here. Seems that the way these work is by completing a circuit between the two terminals. I’d need some kind of device to plug into the outlet that would basically just complete a circuit (without pushing any power through the sensor terminals) when it is powered on, then I could plug the flood sensor or door/window sensor into it. Does a device like this even exist?


I’m not sure I understand the exact requirements / wish list…

Many smart switched plugs (Aeon Z-Wave Appliance Module, and the new SmartThings or PEQ branded CentraLite ZigBee appliance plug modules) report current energy use in Watts… So they are a great way to determine that the plugged in stuff is drawing power… Except when there is no power…


I’m looking for Smartthings to give me an immediate alert when a non-smart electrical outlet is switched on or off. In other words, my scenario is I have an old-fashioned switched outlet in my house. I hit the switch and the outlet comes on. I’m looking for a device that can notify me that this has happened. I could plug said device into the outlet, but because it will still need to communicate with ST when the power is off (i.e. to say “the power on the outlet has gone off”) it will need to be at least partially battery powered. I don’t believe the devices you listed will work as they require power 100% of the time, although I thank you for the suggestions…

Can you “split” the outlet (ie., a power bar or octopus)? Then you can use various types of relays (battery powered) which could sense power in the other fork).

Or you could put an battery powered induction sensor inline with the hot wire of the outlet (such as Aeon Home Energy Monitor).

Yes, I believe both are options. I’d prefer going with the split outlet approach if possible. Could you point me in the direction of a relay that would serve this purpose?

If I was to go with option 2 (inline energy monitor), are they fairly instantaneous when reporting spikes in power usage?

Thanks again.

I’ll look into the first option… But, by the way, it would be a really easy Arduino + SmartShield project is that sounds like fun. Cost ~$50 to $70 max.

The second option… I have a HEM on a test cable, so I’ll test in a few minutes.

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I have an Aeon HEM v1 … very inexpensive because it’s accuracy is limited by voltage fluctuations compared to HEM v2. Still… not a bad way to monitor your power … and probably good for your use case!

As for “fairly instantaneous”… I’m using Barry Burke’s code with a few edits for the Device Handler, but it definitely isn’t reporting very frequently. I am not sure if the configuration settings can be tweaked.

The Device, however, is an excellent candidate for Pollster, since it is reporting immediately after a Poll Request. How quickly do you need the power-on spike detected?

Pollster is not a bad thing to run in your environment as long as you are not running in frequently on dozens of devices. “Frequently” on one device … no big deal.

@tgauchat Thanks very much for your suggestions. I took them into consideration and started going down this route, then I discovered an alternate solution that seems to work really well.

I was able to accomplish this with a 120v Relay (search Amazon, there’s a ton of them, I got the Zettler one), a lamp cord, and a Z-Wave open/close sensor (I went with Ecolink DWZWAVE2-ECO). I wired the lamp cord to the 120V contacts on the relay, then I got a short bit of alarm wire and connected one end to the NC contacts on the relay and the other end to the external sensor contacts on the Z-Wave open/close sensor. When the outlet flips on, the z-wave sensor shows open. When the outlet goes off, the z-wave sensor shows closed. I was then able to use the built-in smart apps to alert me of these conditions. Works great and seems very reliable.

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I am using two devices in my house to know when power is off.

The first is the rev one of the SmartThings PIR motion sensor. It has a mini-usb power port on the side. I then wrote a little app that senses when the motion sensor switches from 110v AC to battery.

The other is a mimolite. It sends an event as it’s going offline due to power loss.

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Perhaps the new hub can be used to do this also? The issue I have with using the V1 ST motion is that it doesn’t detect when the power goes off and comes back on quickly. However all my smart bulbs sense it and all turn on. There are apps that will turn them back off after a power outage, but I can’t find a device that can detect a fast power restoration.

The MimoLite will detect quick power cycles. It’s not cheap (@ $90) and may seem like overkill, but you can use for a lot of other purposes at the same time.

I am using one as a doorbell notifier. I just wired it series with the bell button circuit and placed the MimoLite body in the bell housing. When someone pushes my doorbell the circuit gets powered and when they let go of the button, the power is removed and the MimoLite fires off the power loss message. My app subscribes to the “power off” message. I have it send me a push someone is at the door.

In the case that you’re looking into (cycling bulbs), you would edit the app to subscribe to both “power off” and “power on”. Set an attribute value on the power off side and when it powers back up, check that state value. If it was “off”, then run the routine to turn your bulbs off.

I’ve over-simplified here but you can see the basic logic involved.


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Interesting solution.
I am looking for something to connect to an outlet on an HVAC auto switch outlet.
This would then tell ST to turn on a remote outlet for a remote fan at the other end of the house.
Suggestion for safety reasons, use an old 5V USB charger you no longer need and plug that in and use a 5V relay. (Or 12v walwart and relay.)
Thanks for the idea.

Have you thought about an electric eye to detect the light coming on? That could then notify you some how. Just a thought. Not shur of the how.