Tool to determine if power is off
TL;DR: is there a tool that will let me know for sure the power is off to a light fixture?
I have a 120 year old house that was divided into apartments for much of its life, so the electrical panels are somewhat Lovecraftian (incomprehensible terrifying and sanity-destroying monstrosities with tentacles everywhere. The electrician who upgraded part of one of them when we restored the kitchen said it’s safe, so my question isn’t about that.
We have an outside spotlight that comes on when it wants to, and blinks like it is conveying Morse code, so I’m going to replace it. I know the game with the breakers (one of us in the basement flipping breakers and yelling “well?” and the other near the plug/switch/fixture in question yelling “not that one!”).
Because the spotlight is so temperamental, I don’t trust it to inform me accurately if the correct breaker is off. Is there a tool I can use (maybe a multimeter?) to be sure the power is off before I touch the wires?