Mystery Device, Can’t figure it out!


Very happy new user. Had sense for about 10 days now and have about 14 devices detected. I love getting the notification of a new device! If it says stove, I run over, turn it on or off a few times to confirm it is in fact that device and then fill in the model details on the device tag. Fun!

However, I had a new device pop up about 3 days ago and I am baffled. I cannot figure it out. It named it Fridge 3 and it starts off with a significant power spike of around 850 watts. It then quickly drops to around to 56 or so watts for around a 1/2 hour or so about every 3 hours.

I ran to our main fridge Sense had already identified and unplugged it thinking it may have been a defrost mode or something. Unplugged the refrigerator and to my surprise, the correct fridge bubble went out right away, but fridge 3 stayed lit and was still on. So I ran downstairs to our family room where we have a second fridge thinking that was the device and unplugged it. However, that wasn’t it either. So then I thought given the unusual every 3 hours or so pattern, maybe it was one of the circulator pumps on our boiler. I then went to the breaker panel and killed the power to the boiler. Nope! Fridge 3 continued to stay on and according to the watt usuals, still using about 56 watts steady.

So the next night, Sense notifies me that fridge 3 has turned on. I jump up and much to my family’s chagrin, I start shutting off every breaker in my panel. In an an embarrassing admission, I’ll begrudgingly admit in my determination and rush to figure out this mystery device, I did turn off my dryer breaker which has my sense on it. Doh!

So take two about 3 hours later, all breakers except the Sense. Fridge 3 was still on! Then I thought it had to be something on one of the 2 ups’s I have on some of my equipment. So I ran to each of those devices and turned the ups’s off. Fridge 3 still going steady at around 56 watts! Arrggghh.

Since my dryer is a Samsung with smart diagnostics and I couldn’t kill that breaker, I unplugged the dryer thinking maybe it was the dryer somehow, but fridge 3 remained powered on.

So the only thing I haven’t been able to eliminate is the power to my WiFi router and cable modem. I doubt it is those two items though as this almost looks like some kind of motor. If I had to put money on it, I’d guess the circulator pumps, but when I kill the power to them, fridge 3 keeps going steady!

What can it be? I’ve enclosed a screen shot for review. Thanks in advance!


Your story of trying to identify devices is funny and probably common to Sense owners. My wife thinks I’m nuts, so I wait until she is away do behave like this.

The screen shot looks like this is a classic signature for a circulating or sump pump. Running only 56 Watts (after the start up spike) looks like a small one. The frequency of running appears very regular which imply it isn’t driven by external stimulus like the temperature. However, the length of time it runs has that anomaly at 6am which implies something is telling how long to run other than a timer device. I doubt it is a frig. My guess would be a sump pump.

Just food for thought.
Good luck and when you find out what it is, please post the answer.


Ah, just had another thought. Do you have a radon mitigation system in your house? I think they contain a small motor that may fit your signature.

Can anybody with one comment?


Other thoughts: sand mound sewage have pumps, basement toilet below sewage lines have pumps… and so on.


Do you by any chance have a spa or pool. Sure looks like some kind of small circulator pump.


I do, and it does run pretty much like that, but Sense hasn’t detected it at all.


We have a septic pump, but it doesn’t run regularly like this…it runs when it needs to. I’d assume the same for things like toilets. This is clearly something on a timer.

One device we have that could have a similar signature is an ERV (Energy Recovery Ventilator), also not found by our Sense. Those run regularly based on what its controller tells it is the needed air exchange schedule.


One thing to keep in mind is that the off signature of a breaker throw is sometimes different than the off signature of the device’s internal controls. So turning a breaker off might not cause sense to mark the device as off, and it will need to time out after a few hours. You could, however, look for an exactly 58w decrease in usage on the real-time display while turning breakers off one by one…


Hi All,

Thanks for the suggestions and help! I do have a sump pump, but according to the kill-a-watt I have plugged into it, it hasn’t turned on once since I reset the breaker that outlet is on.

No pool, but I do suspect it is one of the four (or maybe each one of them at different times) circulator pumps I have on my boiler. However, unless I am seeing a display anomaly, multiple times while looking at the real-time display usuage for this mystery device and flicking the breaker off, it keeps ticking right along using power.

Is it possile due to the low power draw that Sense is missing when I am killing the power to the circulator pumps? In my brief experience, pulling the devices power plug, or turning breakers off, has been a pretty accurate way of identifying a device.


I just replaced our radon mitigation fan up in our attic 2 weeks ago but believe these are designed to run continually. About 50W as part of our Always On. IIRC, the older one was using over 70W.


Flipping off the breaker likely has a different “off signature” than the standard off cycle of the circulator due to the timer or whatever. So you could flip the breaker off and Sense wouldn’t see it as an “off event”. Sense will eventually do a time-out on that device based on some function of the typical runtime.

BTW - Sense hasn’t yet found my hot water circulator that is on an electronic timer, so I connected it to a HS110 smartplug.


Yes, pswired agrees as he posted it above, yesterday. I agree with both of you. ;- )


Mystery Solved

It was in fact a fridge! A small fridge we have for the kids in the family room. It was as pswired suggested and I guessed, with some of the lower power consumption devices, throwing a breaker or turning a light switch off does not always result in an “off” event in Sense. I’m guessing Sense sometimes misses the off event in all the noise. Pswired’s advice of looking for the exact wattage change in the real-time display was the trick.

Thanks to pswired and kevin1, and all of you for the input and suggestions.