I use my thermal camera (FLIR E4) all the time. Mostly for electrical inspection, but I've also used it to find a wasp nest in a wall, and see that a hornet's nest was dead or alive.
I've tried it to identify leaks. It can be helpful a LITTLE, but it won't pay for itself that way.
Hmm. How thick was the wall? I’ve been trying to locate a wasp nest between deck planks and a dry deck.
Would one of these find the joist under carpet and plywood flooring? I would like to stop the squeaks.
Why not the Flir for you cell phone? It's a lot cheaper.
https://www.flir.com/products/flir-one-gen-3/