Abstract: A system and method for tracking a number of subjects in a plurality of areas is shown to include a plurality of transmitters, wherein at least one transmitter is associated with each subject, each transmitter transmits a light based signal representative of an identifying code unique to that transmitter, a plurality of receivers, wherein at least one receiver is associated with each area, each receiver converts transmitted light based signals to electrical signals and validates the electrical signal to determine whether such electrical signals are representative of the unique identifying codes associated with the transmitters, and a central processing member, connected to each of the receivers, for recording those electrical signals which are representative of the unique identifying codes for recording the receiver which determined that such electrical signals are representative of the unique identifying codes associated with the transmitters and for determining in which area the transmitter is actually loca

Abstract: A system and method for transmitting an identification signal include a triggering device for periodically generating an enabling pulse signal at random times, whereby the periodic generation of the enabling pulse signal varies in each period in proportion to light incident on the triggering device and a transmitter for transmitting an identification signal in response to the enabling pulse signal. It is preferred that the triggering device include a timer for generating the enabling pulse signal in a defined time cycle in response to a control signal and a signal generator for variably generating the control signal within the defined cycle, wherein the signal generator includes a light sensitive component for varying in time the generation of the control signal in proportion to light incident on the light sensitive component for a portion of said defined cycle.

Abstract: A system has individual infrared radiation transmitter assemblies which issue characteristics and coded identifying signals in infrared radiation, so that transmission and identification of a plurality of distinctively characteristic signals is accomplished by varying the timing of various periodic transmissions so as to avoid interference among the plurality of transmissions. A receiver assembly receives and decodes binary numbered codes sent from a plurality of the individual pocket-size transmitters for keeping track of the location of the transmitters within an area monitored by the receiver assembly. Each transmitter assembly has a timer which periodically variably issues electrical pulses within a predetermined time cycle. The timer actuates a clock oscillator to cause a code stored memory to be read out as coded electrical signals representing binary information and a light emitting diode converts the coded electrical signals into infrared radiation pulses representing the same binary information.