| CPC G01R 22/068 (2013.01) [G01R 22/06 (2013.01); G08B 17/103 (2013.01)] | 14 Claims |

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1. An ancillary apparatus arranged to be mounted on an electricity meter which comprises at least one primary port to which the electricity meter applies a supply voltage, the ancillary apparatus comprising:
at least one secondary port arranged to be connected to the at least one primary port when the ancillary apparatus is mounted on the meter, the ancillary apparatus thus being electrically powered by the supply voltage; and
a secondary processing unit arranged to transmit at least one message to the electricity meter by modulating a supply current of the ancillary apparatus that is produced by the meter and flows via the at least one primary port and the at least one secondary port.
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