My Parents New Invisible Fence

My parents recently just purchased an invisible fence for their yard. It was something I have never heard of so I was interested to learn about it. They live in a neighborhood which does not allow fencing. So if you are a dog owner, you have to set up an invisible fence to keep your dog in your yard. The fence works with an electric transmitter collar which the dog wears around its neck. There are wires buried underground. If the dog steps over the wire, then the transmitter gives off a shock or some make a sound. It is really a neat product they have on the market and I am glad my parents were able to find something that works well for them.