Obviously, for a reason I clearly don’t understand, most, of not all?, temperature sensors use battery.
I’d like something more sustainable, powered using domestic current, ideally zigbee or zwave.
Do you know such a device?
The purpose is to trigger a fan, depending on local temperature.
I use ZWave sensors: Aeon Labs Multisensor6 (ZW100). They can be powered with batteries, but you can power them via a USB connection as well. Which is what I do.
Ahum.
Wemos d1 mini + tasmota + bme280 + 3D printed case.
Best solution ^
After you do this, after a while you’ll understand that now you can also create any other sensor.
So, again, wemos d1 mini + ikea vindrikting pm25 sensor + tasmota = cheap particle sensor.
Or light sensors, presence sensors, Bluetooth sensors… oooff. Tons of stuff.
If they’re available where you are, I suggest a Broadlink RM Mini 3. It’s meant to be an IR remote, but you can buy it with an optional USB cable that has a temperature/humidity sensor. Works great for me.
There’s no official binding, but the unofficial one has been perfectly reliable for me.
Shelly HT sensor sensor with usb base. A WiFi open sensor that you can let me tilt power if your don’t with to build.
While I have no problem building I don’t have a 3d printer, so they always looks a little budget.
I am using a Sonoff TH16 flashed with Tasmota for this. It also has a switch included, making it the perfect device for my pool pump.
Argh, it appears Sonoff THxx are no longer available 
There is a new TH device coming soon (TH Elite), but not as simple/cheap as TH10/TH16.
Shelly HT is a big … big 
and has less advantages as Sonoff which contains 2 features I’m looking for: a temp sensor and a relay.