| 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 signal received from a base station to generate a data signal for 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 received signal, the second receiver element and the processing means not being energised from the internal power source. The first receiver element is responsive to detection of a received signal to trigger an active state of operation 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 characteristic of the signal received to actuate the processing means. The invention is applicable to access control systems, especially to vehicle access control systems, and also to tyre pressure monitoring systems. <IMAGE> |
