Apparatus for monitoring an ECG signal comprises a first body wearable part 1 for receiving a physiological signal and comprising processing means, a memory, and a wireless transceiver, the memory storing a plurality of signal segment templates. The processing means is arranged to compare and match segments of the physiological signal to the stored template. The apparatus further comprises a second part 4 comprising a wireless transceiver and processing means, the processing means being arranged to generate and/or modify signal segment templates, and to cause said transceiver of the second part to transmit generated or modified templates to the first part.