Component that activates a switch when charged?
You can take the AC and peak detect it to turn on a logic level MOSFET.
Size R1 to adjust the turn on and turn off delay according to the frequency of the signal.

I'm concerned your AC voltage may be a lot higher than your meter is showing you though, so I added a 5.1V zener, D2, to protect the MOSFET. 

HOWEVER : If the output you are measuring is the shock voltage, it will be in the killo-volts range so don't even think about hooking this up.







simulate this circuit &ndash; Schematic created using CircuitLab