Embodiments disclosed herein relate in part to water flow sensors, and also to such water flow sensors in combination with a system used to selectively shut off the flow of water through a water supply pipe to a building, such as in the event of a broken water pipe. One embodiment includes a message waiting system that identifies a failed delivery attempt of a text message to a mobile device that is unavailable, where the text message originated from an external message center. The second component has a second linear polarization and a second frequency.