PASSIVE COMMUNICATION DEVICE AND PASSIVE ACCESS CONTROL SYSTEM

摘要

A communication device comprising an internal power source, receiver means for receiving signals transmitted from the base station, and processing means selectively responsive to an interrogation signl received from a base station to generte a data signal fro transmission to the base station. The receiver means comprises a first receiver element and a second receiver element, the first receiver element having lower power consumption than the second receiver element does when energised. At least during a standby state of the device, the internal power source energises the first receiver element so as to detect the presence of a entergised from the internal power source. The first receiver element is responsive to detection of a received signal to trigger an active state of oepration of the communication device in which the internal power source energises the second receiver element so that the second receiver element is selectively responsive to a characteristice of the signal received to actuate the processing means. The invention is applicable to access control systems, especially to cehicle access control systems, and also to tyre pressure monitoring systems.