Blew $180 on a thermal camera and it found the one bad panel before the drywall went up
Bought a FLIR One for $180 back in March mostly to look at attic insulation, but it paid for itself on a job in Tempe when it showed me a hot spot behind a freshly nailed panel. Turned out a staple had nicked the romex and it was arcing just enough to warm up. What is the cheapest tool you have bought that ended up saving a whole callback?