| 摘要 |
A global navigation satellite system GNSS tracking unit is disclosed comprising a GNSS receiver, processing circuitry and a radiofrequency or other transmitter adapted to transmit at least location data relating to the unit to a remote receiver, wherein the transmitter is provided with a controller linked to at least one sensor, and wherein the controller operates to cause the transmitter to transmit when the at least one sensor detects a predetermined event, but to refrain from transmitting at other times so as to hinder detection of the tracking unit by unauthorized monitoring of transmitted signals. In a further embodiment, the transmitter is arranged to transmit at pseudorandom time intervals which may be spaced from each other by at least 5 minutes. |
