A biometric authentication system comprising headwear comprising a plurality of biosensors each configured to sample muscle activity so as to obtain a respective time-varying signal; a data store for storing a data set representing characteristic muscle activity for one or more users; and a processor configured to process the time-varying signals from the biosensors in dependence on the stored data set so as to determine a correspondence between a time-varying signal and characteristic muscle activity of one of the one or more users, and in dependence on the determined correspondence, authenticate the time-varying signals as being associated with that user.