I noticed the same on all in Aqara Zigbee temperature/pressure/humidity sensors. They're all inside, I could still easily see it twice (many hours apart). Though I only noticed after someone in a Home Automation topic mentioned seeing the effect ;)

Nothing fancy was needed for this, the sensor I'm talking about is battery operated. I have this one: https://www.zigbee2mqtt.io/devices/WSDCGQ11LM.html or this one: https://www.zigbee2mqtt.io/devices/WSDCGQ12LM.html (they look alike too much).

It's a Davis Vantage Vue.