Thermal imaging system
Thermal imaging -- looking for "hot spots" or other temperature differences has many uses. Home energy auditors do this to see where you need more insulation, better windows, etc. Industrial sites use them to spot anomalies before problems develop. They're popular for security monitoring, gas leak detection, and with firefighters. But traditional thermal imaging systems haven't been cheap.
FLIR One's case will let a smartphone act as a thermal imaging system, showing infrared, even merging it with regular camera views and other data.