A cord-based controller for an auxiliary device, such as a headset, is provided for use with a portable electronic device. A pressure-sensitive, and preferably bendable, material such as a piezoelectric pressure sensor is placed within or on an or cord of a headphone lead, such as by wrapping it within the outer shielding of the cord. A self-powered controlling sensor is arranged to control the electronic device using a generated control signal. The controlling sensor comprises a sensor material. The control signal is generated by deformation of the sensor material independent of power supplied to the headset and independent of power supplied to the portable electronic device. This is achieved without requiring a separate housing for the controller, which typically protrudes from the cord. A plurality of control sensor elements can be provided, each producing a different control signal voltage transmitted along a single control signal electrical.