The box must be hard wired to the AquaTrip Control Unit so that if the water has been switched off due to a leak, the user can press the reset switch and turn the water back on again without accessing the Control Unit itself. There can be any number of reset boxes connected to one AquaTrip. Requires optional part # PBC-AT to connect to the AT201 model & optional part # ANT2-0N or ANT2-3N to connect to the AT301 model - a simple plug in connection. The AT401 model does not require anything extra.