PetSafe Outdoor Bark Control

Hang or place this device outside to deter nuisance barking by emitting an ultrasonic sound. There are four levels of operation so you dial the level that has an effect on your dog. It detects barking up to 15 metres which means you can even deter your neighbour's dog from annoying you! Uses one 9 volt battery - sold separately.

Note: The image shows 2 devices - they are sold as individual units.