A method of controlling a wireless power transfer system. The wireless power transfer system comprises an electromagnetic induction charger operable to emit electromagnetic radiation into an environment of the charger, motion sensor equipment operable to generate an output indicating whether or not a moving object is present in the environment, and a controller. The controller is configured to receive the output from the motion sensor equipment, determine whether the received output indicates that a moving object is present in a predefined region of the environment, and in response to a positive determination, prevent the charger from emitting electromagnetic radiation.