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?
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.
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.
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.