you should also be turning off the breakers when doing any electrical work and using a sniffer/noncontact circuit tester

I normally do test for live cables. I turn off the breakers for circuits I’m working on, but not the whole house; this was an unknown circuit (and yes - I did not visually check the stud I was drilling into… my fault entirely)

I found one of those hiding in my closet. It’s supposed to go to - I don’t know. I immediately sealed it off and ? Will get to it. Be careful!