This document discloses an apparatus (100), such as a smartwatch, comprising: a radio frequency radiator circuitry comprising an elongated radio frequency resonator (104, 106, 108, 110, 114) and configured to generate an electromagnetic field extending from the radio frequency resonator; a measurement circuitry configured to measure an electric property of the radio frequency resonator responsive to a proximity of an object (210), when the radio frequency radiator circuitry is generating the electromagnetic field; and a processing circuitry configured to convert the measured electric property into a user input command. In other word, said apparatus functions as a radio frequency based input device.