Abstract: A system and methodology for a programmable and reprogrammable locating system comprising of at least one central control unit and at least one response unit. The central control unit, for activating the response unit and for programming/reprogramming the response unit, utilizes a serial bits stream signal to communicate the programming data and activation data to the response unit. Both the central control unit and the response unit utilize the generation of a square wave for discriminating between a signal as coming from a central control unit from those signals emanating from non-central control unit sources. This signal discrimination capability and signal data carrying capability allow multiple response units to be programmed/reprogrammed to one or more central control units.