I found with my dog when I follow the normal instructions about how snugly to fit the collar, it often ends up too tight and sits at a slight angle on his neck bones and makes unreliable contact. It's also incredibly hard to find his lowest working level if there's no clearly obvious muscle twitching. He will only respond to a test stim with the usual ear flick, air lick, etc. exactly once. I have to wait a few minutes to try again and confirm he's actually feeling it.