Sensor to tell me when something looses power

Sometimes I loose power to my deep freeze and i am wondering if anyone has some kind of setup or sensor that could help. Is there maybe something that the freezer could plug into that could just let power through but trigger a warning when it detects that power is lost to the outlet?

If you have a strong zigbee mesh, then there is the Xiaomi temperature/humidity sensor which can be programmed to send out an alert under those conditions.
If you don't have a zigbee mesh, there are other zwave plus sensors that do more or less the same thing.

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This thread may offer you some options.

And here is another idea that I came up with...

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I have a suggestion that doesn't require building anything electronic. It may seem a little hokey but the principle is sound.

Using a DC electromagnet to hold a simple Z-Wave / Zigbee contact switch in the closed position. With the loss of power the battery operated contact switch (there are many for doors and windows) will send an "open" signal to warn you of power loss at that outlet.

!!!!! UPDATE !!!!!! I just performed a test with an Aqara contact sensor magnet using a magnetic field film. The N and S poles are at the ends (long dimension) of the magnet. This means it will near impossible to use a typical electromagnet to directly control the contact switch (at least the Aqara). Perhaps the solenoid is the best approach.

I've not built one so you may have to do some playing with the details.

My thoughts of a BOM:

  1. Electromagnetic: Must be designed for continuous duty, or perhaps a 12V magnet operated a 6 or 9V would work. Amazon and Ebay have many.

  2. An AC adapter for the above. 12V or maybe lower.

  3. A Z-Wave / Zigbee door / window sensor.

If you can't get the electromagnet to operate the contact sensor directly, you might have to use a weight being held by the electromagnet which when released would remove the sensor supplied magnet away from the sensor.

I guess you could also use a small solenoid and a spring. Or maybe just a solenoid pointed down so when the solenoid pole piece drops out the Door contact magent is moved away from the sensor body. Perhaps this device. Solenoid

You could use a mains solenoid but that would require some mains wiring, with the wall wart everything is operating at safe voltages.

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Thanks for the suggestions. I guess it looks like there is not really an easy buyable solution to this problem.

Sorry I don't have an answer to your question, but what is causing your power loss? Are you tripping your home circuit breaker? Is the freezer plugged into a GFCI outlet that keeps tripping?

@bobby Could you just do this? I assume the circuit loses power right?

Get something like a Zooz current monitor, they make a heavy duty one that goes to 15-20 amps. Monitor it for current/power/voltage/what ever, it's actually not important.

Now you're going to say, but it loses power dummy, I can't monitor it! But aha! When it DOESN'T reply you've lost power.


How can you detect "does not reply" in RM?

I can see how you could write a driver for that, like a simple, single device version of Device Watchdog, just to ping it at the network layer periodically, or do a refresh, and change state if no reply in $threshold seconds.

I have a ZigBee Door sensor that also senses Temp in my Freezer. I have had this in my freezer for over a year now. I have a Notification App setup to notify me if Temp is higher then X. Been working great.

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I have same setup with iris close/open sensor measuring temperature and also checking if door is not open too long.
Battery last over year even inside freezer



Yup I'm going in about a year and a half on battery. Easiest way to make sure freezer is still running.

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I have Iris v2 Motion/Temperature Sensors in my two refrigerators and freezers. I have a rule that notifies me if the temperature rises above a certain level. If you’ve ever had an issue with a refrigerator door being left open, this is a solution. I prefer this over using a contact sensor, because that just looks too ugly.

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It is plugged into a GFCI outlet. I know the instructions say not to but you go to war with the outlet you have, not the outlet you want. plus it only blows about once or twice a year.

I did end up just buying a power off siren that plugs in to the same outlet. In my heart I want everything to hook up to my home automation system, but in my head I understand that not everything has too. But I am going to look into the temperature monitor. I didn't think one would be able to transmit out of the freezer.

How old is the GFI? Technology has changed in recent years and they are much better than they used to be. I had one in my garage that controlled all my outdoor outlets and it started tripping more often. I replaced it and so much better.


Its from the 80's, it controls the garage, back yard, and both bathroom. I'll looking into changing it, thank you.

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My downstairs powder room was on my garage/outdoor circuit and rain during holidays would trip my GFI as my outdoor lights got really wet. This was super annoying so I moved my powder to another circuit. Fortunately I have a crawl that made it easy but something to consider if you are able.

We found that the best way to reliably monitor power loss in real time is through a simple 12 VDC power supply connected to a Z-Wave dry contact sensor, more details here:

Aeotec discontinued their dry contact sensor but they added this functionality to the latest Door Window Sensor 7 so that should work here.

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You do something like this, works with Zooz plug pretty nicely

  1. refresh() on device
  2. wait event device, energy duration or timeout
  3. If energy duration > last energy duration == OK
  4. If energy duration < last energy duration == Power failed, but returned
  5. If energy duration == last energy duration == power out now
  6. Save to energy duration to local variable

if would be really easy if something was set to indicate timeout on wait condition/wait event.

If you can't do energy duration, energy, kWh is the same....maybe that works better. Both are resetable so you could just reset them to 0 and make sure it's incrementing and readable.

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There are a few variation of this method in the post that @ogiewon linked to above. Some have retrofitted a Samsung leak sensor and other like myself have used the Ecolink contact sensor that has extra screw down connectors that can be used to connect wires to a relay. A LOTsimpler than it sounds and it has worked reliably and instantly for me...without fail. Below is a link to the same post but further down into the thread where simpler options are discussed (the initial discussion is a bit more technical).