Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Worthless

I purchased two of these units. First of all, the range between the transmitter and receiver is more like ten inches; not six to ten feet as advertised. And, our dog walked back and forth right next to the unit with no response. She finally trained herself to stay out of the room being "protected".I wrote and phoned Lentek with no return contact from them. I have purchased their products before, but this will be the last time.