We have tried a non bark collar that gave two warnings(long beeps) and then would give a shock if the dog keeps barking. It worked really well, but, when someone he didn't know came in he couldn't control himself and...well....it was quite the scene. No more collar. I found this, it uses a high pitch frequency, like that of a dog whistle. Has various settings for distance and testing. It works the first time. Bark, little red light flashes letting you know it's putting the frequency out. And my dog noticed right away too. Didn't like it and went and barked about it far away!