Amazon.com: Pet Parade's Dog Repeller, Black...
here is some info about it
Eliminates barking and annoying behavior by emitting a piercing ultrasonic tone that pets hate, but humans can barely hear. Stop dogs from jumping, barking and biting
I would definitely recommend It for Barking
Well Yesterday I took it outside when it was Polo's potty time, and he saw a dog he goes crazy and starts barking. I pressed the button for about 5 seconds he tilted his head looked at me like WHAT THE HECK and Completely stop barking.