A signal receiver capable of operating in two modes: a normal mode for reception and decoding of signals and a detection mode for detecting the presence of signals, the signal receiver having: a functional unit that can operate in two manners: a first manner having relatively low power consumption and relatively poor accuracy and a second manner having relatively high power consumption and relatively high accuracy, and a controller for causing the functional unit to operate in the first manner when the receiver is in its detection mode and in the second manner when the receiver is in its normal mode.