Abstract: A system and method for detecting when a satellite is within range of a small, battery-operated, portable transmitter so as to activate the transmitter only when the satellite is within range of the transmitter. The electronic system utilizes a sensitive radio-frequency receiver which can be tuned to receive a unique down-link signal from the orbiting satellite. The signal is amplified and demodulated and then input to a microprocessor. Information is stored in the memory of the microprocessor which identifies the unique down-link signal. The microprocessor compares the demodulated signal with the stored signal and if the two match, the earth-based transmitter is turned on and allowed to transmit for an interval of time. The microprocessor is maintained in a normally "full-stop" mode wherein power to the microprocessor is essentially turned off, and the microprocessor is periodically switched on so that it can check for the presence of the uniquely identifiable down-link signal which triggers transmission.