My 3 attic fans are not controlled by a smart switch. They go on and off on there own based on temperature and humidity. Are there any zwave or zigbee sensors that could tell me when a fan is on or off? Maybe something that measures current?
Thanks
Dale
Are they hard wired, or plug in?
There are small plug in outlets that provide current:
https://www.amazon.com/dp/B08P3T48MD
https://www.amazon.com/Aeotec-Switch-Wireless-Control-Automation/dp/B08PKLBKW4
I have a couple of the Aeon ones, before supply problems caused the price to skyrocket, that are doing this current measurement (Power/watts actually) on my Washer and (gas) Dryer to tell me when the Laundry is done.
Choose wisely because they have fine print on the maximum power. They will shut off if the power exceeds their limit. I had an different product that had a 13amp limit that tripped a couple times. Had to replace it with the Aeon's to get the full 15amps.
On/off is easy - you need a current sensor switch with dry-contact output that is connected to a contact sensor.
To measure current you need a current sensor that is compatible with Hubitat, unless these are 120V fans in which case the outlets @csteele indicated would be perfect.
Thanks guys. Currently (no pun intended) they are all hardwired, so it would take some work installing outlets. I was hoping there might be a sensor that wraps around the wire.
There are current sensors that are Hubitat compatible, but you'll have to separate the load conductor from the neutral conductor. And place the current sensor only around the load conductor.
Here's an example of a current sensor that can monitor two of your fans (it has two CTs):
Could use an Aeotec Door switch (or similar) that has external dry contacts, and a “sail switch”, which would sense the air motion: Suburban Furnace Sail Switch 233100 | pdxrvwholesale
How about one of these?
Connect it to a Ecolink contact sensor.
I put them in my shopping list, when I saw a thread on somewhere 0n here and thought one might come in handy, but have yet to find a use.
How would you use the Ecolink Contact sensor with this? Wouldn't it be more like the switching bit (SW) of a relay like the Zooz Zen16 or 17? Or maybe one of the smaller ones depending upon the load etc.
https://www.getzooz.com/smart-relays/
Very cool find btw.. bookmarked as well!
Simple motion sensor(s) pointing up at the fan blades?
Wind might trigger that?
Yeah...only works if the fans are stationary when not under power. No idea if that's how these would work, but like a simple/lazy solution. 
He could set a minimum time moving to report active that might avoid false positives from intermittent wind.
Can a regular motion detector (a PIR device) pick up a fan? Even after the fan warms up from running, there'll likely be no differential between the two PIR sensors in a motion detector.
Edit: The answer is in. I tried two PIR motion sensors (Aqara and Hue Indoor). Neither of them detects a fan moving.
Garage door sensor mounted on the fan blade. When it quits going OPEN/CLOSE/OPEN/CLOSE... you know its off. Just kidding. It would saturate the airwaves and probably fly off and kill something.
What about the zooz tilt shock sensor. If thr fan creates enough tubulance it could be triggered.
Maybe even mont to the fan. Just make sure it can't come off and doest create a balance issue for the fan
OK, now you got me. 
I'm bummed...just don't have a McGuyver brain. 
Maybe if he glued a stags head, facing down, to the hub of the fan...those antlers whirling around would set off the darn sensor!
If I understand it closes the relay when power is applied. The Ecolink sensor has contact points you can wire to. So when the relay closes the contact closes, fan is on, when open fan is off.
Edit: Never had read through the complete literature, but it looks like it requires the contact to be tied to a load so I guess it wouldn't work for this scenario, or as I had envisioned using it.
Okay so you are seeing the same thing I was.. you could still use a relay though. The idea would not be to digitally turn things on/off but to detect on/off via the the Current Switch.
That will definitely work. I use a similar current sensor (from Functional Devices) to detect when my HVAC blower is running/off and use that to directly control an in-duct blower (no Hubitat involved).
I also have the current sensor connected to the external terminals of a GoControl contact sensor so I can raise/lower Sonos volume based on the HVAC blower state (automation through Hubitat). If I didn't have plenty of unused GoControl contact sensors, I would have used the Ecolink you suggested.
The first setup (in-duct blower) has been working for ~7-8 years without issue. The Sonos volume setup has been working for ~2-3 years, also with no issues.
Your suggestion is definitely one of the most robust ways to detect whether an electrical device is in use or not. And not difficult to setup.
@erktrek (and also @daleberlin)
Here's an example using logs of the setup that @terminal3 suggested:
HVAC turns cooling on:
It takes the blower about 20-25 seconds to be energized. Here's when the contact sensor connected to the current sensor on the blower closes:
Similarly when the HVAC turns off:
The contact sensor turns to "open" within a few seconds (the HVAC blower is programmed to run for 30 seconds after cooling is turned off):
So my Hubitat automation is to raise the Sonos volume when the contact sensor closes, and decrease it when the contact sensor opens.
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