A method of sensing the presence of a body from a change in an amount of charge present on a capacitively charged key. The method comprises inducing charge onto the key during a drive part of a measurement cycle, coupling a signal measurement capacitor to the key during a signal measurement part of the measurement cycle to the effect that the charge induced on the key during the drive part of the measurement cycle is transferred to the signal measurement capacitor, determining from a noise measurement part of the measurement cycle an amount of charge induced on the key by noise during the signal measurement part of the measurement cycle, and controlling the drive part, the signal measurement part and the noise measurement parts of the cycle to provide the charge sensing circuit with a measurement of the signal from which the noise induced on the key has been or can be substantially cancelled.