Power Circuit Monitoring for Power Loss

Looks like you are missing the jumper wire between the dc+ and the in on the relay.


Like so, assuming the left is dc+ and the right is "in".


Thank you both. Solved. Duh!

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Been searching for this an didn't encounter anyone talking about it so far (could be my search skills failing) ... but does it seem reasonable to use a SmartThings Arrival Sensor?

When I was browsing a thread about presence, folks started talking about battery hacks for the arrival fob and it occurred to me that you could use a 3v wall-wort instead of AA batteries. So when the power goes out, that's basically just the same as a departure right? I guess it would have the 15sec delay, but I'm guessing most folks with HE on a UPS could last longer than that :slight_smile:


I’ve just updated my app to be able to use presence.
The alternative to using an ST presence sensor is to ping and old router or similar that is not connected to a ups.
Then when the power goes off the presence will be set away and will trigger my app.



You could use a ring range extender .. It has a battery backup and will report mains power loss

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and they are on sale for $18.75

Ring Alarm Range Extender https://www.amazon.com/dp/B07FQ6SDKY


I'm trying to accomplish A/C loss power down with no additional hardware. This is more a challenge than reluctance to add hardware. Although I will admit I try to limit battery operated devices where ever I can.

My hub is powered by a very small UPS that should last 2 hours or more.

And I have a number of A/C powered devices that when refreshed return some response. I was planning on using two of them to determine loss of power:
One device would be polled say... every 10 minutes and if no response then check the 2nd device. If neither responds I'll assume A/C power is lost so I wait an hour or so and then shutdown the hub.
No extra hardware is needed. My UPS is automatic so waiting 10 minutes (or even 15 minutes) to realize power was lost is not an issue.

Actually I'm still testing the UPS and will report what I end up with when I have completed testing and have some hours on it.

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What attribute do they use for power loss?
I can easily add this as a trigger to my app.



Using powersource:


Device Selector


Driver Definition

capability "PowerSource"


powerSource - ENUM ["battery", "dc", "mains", "unknown"]

So it will switch from mains to battery


I always try to keep my drivers as pure to the capabilities as possible.. For interoperability with other automations


Thanks @bcopeland !

I have coded the additional trigger and ordered a device from Amazon to test it with.
Hopefully, it should arrive by Friday 17th so I can test properly.
Then I'll release the new version.

If anyone has the device and is interested in testing the code now, then please submit a ticket as usual



Nice.. Can you send me the fingerprint for the uk version for me to add to the driver?

I will :slight_smile:

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Not sure how many Brits would buy it though as it cost £30 here :frowning:

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I am modifying my door sensor to use as a pwr monitor and your picture is not clear. I am connecting to the reed switch vice the terminal block. I have the resistor and red usb wire going to the base (center lead). I have the usb black lead and emitter (left lead) going to the Left hand terminal of the reed switch (unit oriented with battery to right). I have the collector (right lead) going to the right hand terminal of the reed switch. The left hand reed switch terminal is connected to the negative terminal of the battery. Is this correct?
Thanks for your help.

Welcome to the Community. Which picture are you referring to? Many within this post.

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Sorry about the confusion. ! have attached two photos that show connections of the transistor and resistor, but it is not clear where the connections are made. I have made them using a 2n3904 transistor and a 220 ohm resistor with the red 5v lead to the base (Center), the black and emitter (left) to the reed switch terminal closest to the terminal block (whichis also connected to the negative side of the installed battery), and the collector (right) to the reed switch terminal closest to the battery. When I energize the 5V power supply the transistor get very hot and fails. I thought about connecting to the terminal block, but there seems to be no connection from either one of the terminals to th negative side of the battery, so that has me confused. Any help would be appreciated. d3e2cd2fbb133fb11560326572cd87f2441b92f1_2_666x500|666x500

Looks like you may have been trying to replicate @JBrown setup. I personally ended up using a 5V relay like many other folks responding to this thread. Maybe he can help you.

What sensor are you using? Do you have a volt meter?