A method of controlling a personal acoustic device includes generating a first electrical signal responsive to an acoustic signal incident at a microphone disposed at a location on an earpiece of the personal acoustic device such that the microphone is acoustically coupled to an environment external to the earpiece. A characteristic of a transfer function based on the first electrical signal and a second electrical signal provided to a speaker in the earpiece is determined. An operating state of the personal acoustic device is determined form the characteristic of the transfer function. The operating state include a state in which the earpiece is positioned in the vicinity of an ear of a user and a second state in which the earpiece is absent from the vicinity of the ear of the user.