Apparatus measuring biological electrical activity using a plurality of sensors, eg EMG, in contact with a human or animal. A signal injector inputs a reference signal into the body at a frequency different to that of biological electrical activities. The plurality of sensors each detect a magnitude of the reference signal and biological electrical signals. A lift detection unit receives the signals from the sensors, determining the amount of contact the sensors have with the body. A noise cancellation unit weights the signals according to their contact with the body and forms an active cancellation signal by combining the weighted sensor signals. Preferably, the noise cancellation unit removes the reference signal from the signals detected before those signals are combined to form the active cancellation signal. Preferably, the noise cancellation unit suppresses signals with lower contact quality relative to signals with better contact. Suppression of the signals may be determined using thresholds. The noise cancellation signal is injected into the body via the signal injector. The apparatus may be located on headwear eg glasses. The lift detection unit may also identify signal patterns characteristic of one or more facial expressions. Also, a method.
