Thermometers are plenty useful, but they’re something we’ve never really carried daily for lack of one that was convenient and portable enough. Until Thermodo, that is. Tiny, lightweight, and remarkably durable, Thermodo sits on your keyring, protected within its included keychain, until it’s called upon. Then, just plug Thermodo into your Android or iOS device’s audio jack to immediately record the ambient temperature right where you are using their free app, using no external power whatsoever. Its iPhone-matching sandblasted anodized aluminum enclosure ain’t half bad, either.

Grab one at Amazon – $35+