| CPC E21B 47/16 (2013.01) [H04Q 9/00 (2013.01); H04Q 2209/883 (2013.01); H04Q 2209/886 (2013.01)] | 18 Claims |

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1. An acoustic telemetry unit comprising:
an acoustic receiver arranged to receive acoustic telemetry signals;
a filter arranged to filter signals received by the acoustic receiver;
a processor arranged to process a signal passed by the filter to recover a data signal, the processor being operable in a sleep mode;
a detector arranged to detect the signal passed by the filter; and
a wake-up circuit arranged to wake the processor from the sleep mode when the detector detects the signal passed by the filter.
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