Very easy system to expand. The sensor has to be keyed into the same code as the receiver, much like the channel selector of a wireless phone. After removing the bottom screws and the isolation shim that preserves battery life before use, I keyed it into the same frequency, replaced the bottom and screws and dropped it next to my upstairs toiled bowl. Shutting the water down from any point in my home is a pretty cool premise; well thought out product.