However, remember: Do not correct your dog for not returning right away. (petcarerx.com)
This means that it will only turn on and correct your dog when it feels the vibrations of your dog's vocal cords in combination with its bark. (dogcollarguide.com)
And remember, you can't correct your dog for having an accident in his crate unless you catch him in the act! (thehousebreakingbible.com)