A memory tag comprising a resonant circuit part, a memory, a detector module and an output generator module, the resonant circuit part being operable to generate an output signal in response to a signal from a reader, the amplitude of the output signal dependent on the magnitude of the signal from the reader, the detector module being responsive to the magnitude of the output signal such that, when the magnitude of the output signal is relatively low, the detector module causes the output generator module to transmit an identifier signal, and when the magnitude of the output signal is relatively high, the detector module connects the memory to the resonant circuit part.