I wanted to hang one of these small thermometer/hygrometers on my shop's pegboard, so I could easily see the temperature and humidity. The backside is open, with a spot to hang over a hook, and cutaways on each side to allow easy air flow to the sensor.

Designed to hang from a nail/hook/etc. If you want to hang on a standard pegboard, it works well on this Low Profile Pegboard Hook.