An apparatus including: a radio transmitter configured to transmit radio signals that are at least partially reflected by a human body; one or more radio receivers configured to receive the transmitted radio signals after having been at least partially reflected by a human body of a user; a gesture detector configured to detect a predetermined time-varying modulation that is present in the received radio signals compared to the transmitted radio signals; and a controller configured to interpret the predetermined time-varying modulation as a predetermined user input command and change the operation of the apparatus.