OK.
The most reliable (and least likely to respond to an errant audio signal ) is a simple audio circuit that uses an
LM567 Tone decoder. This device has been around for a
very long time. Basically behind the touch tone phone signal decoding. Its output goes to ground when activated. With an electret mike and a small, medium gain OpAmp amplifier in from of it and, wahla, you have your audio fired switch.
I've had very good success with this device when I needed rock solid audio detection of a specific audio frequency, especially in an environment with a lot of spurious, extraneous and random "noises".
If you're interested, I'd be glad to provide a schematic.