One of the best blogs in the world, Petistic, showcases the Bark Terminator:
Bark Terminator electronic bark control collar has a built in microprocessor that monitors your dog’s barking pattern and automatically increases electronic shock stimulus as barking persists.
A computer chip monitors the wave patterns of sound received by a microphone. This chip analyzes the sound wave pattern received by the microphone and is able to tell the difference between of a dog bark and stray sounds in the environment. This ensures that only your dog’s bark will set off the unit. Because sound pattern and volume are monitored, the sound of other dog’s barking nearby will not trigger the unit.
I can think of a few people I’d like to strap this unit on.