A removable cover for a handheld electronic device, including a protective cover that at least partially covers rear and side surfaces of a handheld electronic device, a plurality of proximity sensors mounted in the cover for detecting user gestures performed outside of the electronic device, a battery, wireless communication circuitry, and a processor configured to operate the proximity sensors, and to operate the wireless communication circuitry to transmit commands to the electronic device based on gestures detected by the proximity sensors.