This is sized for a medium to large dog. ...

This is sized for a medium to large dog. It will not likely fit a small dog. The problem I having is that it will not deliver a shock. I know that it is working having tested it on myself numerous times. My dog has very short hair but it will not shock him no matter how tight I place the collar. When I press the electrodes on my arm wearing a thin shirt it will not shock me so I think it is just not strong enough to travel through fur. If your dog has long or thick fur I doubt it will work at all. The chime and vibration modes do work as advertised.

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