I'm trying to figure out how to notify an Arduino controller that there's been a momentary interruption to a 120V AC circuit that is normally powered. When a spring-loaded switch is pressed, it opens the AC circuit until the switch is released (typically about 0.1 to 0.3 seconds in duration). I don't care about measuring the current, I just need to know if the circuit has power or not.
At first I was thinking a relay would be appropriate, but it seems like most relays are designed to let low voltages control higher voltages, not the other way around.
Using a CT may be a possibility but it's a somewhat cramped area, so it may be difficult to fit a CT in and get it wrapped around the line I need to watch.
What other options might I have?