These collars worked as soon as I put them on 1) 10 lb. Chinese Crested Puff and #2) 35 lb Pitt mix. These little lovies were running across the deck barking at the squirrels especially annoying late at night when they thought they heard something. I don't leave them on all the time, just when they begin the behavior again. It seems to humble them but they don't relate this to me. I use the vibration on 2, and the shock on 0 for the Puff and low for the Pitt. I do recommend.