You could use a heat sensor to check your house for leaks, for instance. But mostly, it's a lot of fun.
It was in an M1A2 Abrams main battle tank that I first discovered how to see properly. The U.S. Army Armor School had invited me to spend a day in its simulator in Orlando, Florida, and, after looking through the commander's thermal camera unit, it occurred to me that I should have one of my eyes replaced by a cybernetic thermal device. The imager allowed us, day or night, to penetrate camouflage and clearly observe adversaries glowing several thousand feet away.
For the past two decades, civilian infrared options have been bulky and expensive, used mostly by fire departments locating people in burning buildings and contractors identifying poor insulation and overheated wires. But thanks to significant innovations in infrared chips, called microbolometers, two new thermal devices are available—and actually affordable—to folks like you and me. And they fit right on your phone.