Products within this family are used to measure or detect the flow of a fluid such as water or air. The simpler products provide a binary indication of whether or not the flow rate exceeds some defined value, whereas the more complex products are capable of providing a variable output from which the amount of fluid flow can be determined as a mass or volume-per-time quantity. Device performance in either case is quite strongly related to the properties of the working fluid, and media compatibility issues are also a matter of noteworthy concern for device selection and application.