A bark detterent collar for use with sensitive/timid dogs.
PetSafe Bark Control Collar - Sonic (for sensitive dogs):
This light, 28g collar emits an unpleasant but harmless tone to correct your dog’s barking problem. The collar’s cutting-edge, bark-detection microphone can be adjusted to recognize your dog’s unique bark so that no other sound can set off the unit. This collar is most effective when used on small dogs.