If your facility does not have ANY internet service, and you want to connect the Hydro-x, Aqua-x or Hawkeye units, the RTU-1 might be the solution for you. The RTU-1 uses a cellular (AT&T) sim card and cellular network to provide an internet connection to our controllers installed in remote locations. If your facility is within range of AT&T phone service, the RTU-1 can be used to link your TrolMaster products to your smart-phone / APP. *Requires monthly service fee from AT&T