It's called a bark box. Our cocker is pretty protective and will bark some even when with us, barks at everything when alone. We picked up a "pets safe" bark box at Petsmart. We chose the one that gives a mild shock only when barking. Took her about 3 barks and she stopped barking when wearing the collar. We always put it on her just before we leave and now she settles right down and goes to sleep. Never have any barking complaints. Normally we don't even have to put in the battery anymore it worked so well and she knows what it is. That's how we handled it, hurt us way more than it did her.
Dave