Here is a jolly cute Bluetooth-enabled sensor-and-digital-clock to monitor your room's temperature and humidity. Only 110mm x 55mm, we dig its medium-size form factor and minimal design. 

The shell is made of durable ABS material. Upfront you get a 3.5" x 1.25" (87mm x 32mm) eInk display. These sensors are sold to work with the Mijia "Mi Home" App (iOS and Android) - they emit the measured humidity and temperature over Bluetooth LE up to about 10 meters away.

And while it's totally fine to use it with the Mi app, we like this more for its use cases in general home automation and sensing projects!The sensor has two modes. One is advertising modes, where it sends out sensor data every few minutes. The advertisements are encrypted so not easy to read. You can also connect to it as a BLE device and read from the sensor characteristic, which thankfully is not encrypted. You can use these with ESPHome / Home Assistant as a remote sensor node. They also work great just as an 

E-Ink clock, note that to set the time you should use this web-bluetooth page that will connect and fix the timezone.

Comes with 2 x CR2032 coin cell batteries (pre-installed), a magnet, and adhesive stickers, so you can mount the clock sensor anywhere you please.