Margaret Rhodes, Co.Design:

Spotter is a white disc packed with sensors that measure temperature, humidity, light, sound, and motion (motion isn’t detected, but rather has to be felt physically through an accelerometer). Install it permanently anywhere, or use magnets or stickies to transfer it around the home at whim. Once Spotter is set up, the app companion lets users dial between actions and create actions and alarms.

A simple, useful, and beautiful multi-purpose sensor invented by Denny Fong. US$50 at Quirky.