Abstract: An acoustic telemetry unit comprising an acoustic receiver for receiving acoustic telemetry signals is disclosed. The acoustic telemetry unit comprises a filter for filtering signals received by the acoustic receiver, a processor for processing signals passed by the filter to recover a data signal, the processor being operable in a sleep mode, and means for waking the processor from the sleep mode in dependence on an output of the filter. An energy storage module may be charged using signals received by the acoustic receiver which are not passed by the filter. The disclosed techniques may help to conserve battery power.