Various embodiments transmit a radio-frequency (“RF”) beam using two or more RF antennas of a mobile device, e.g. a mobile phone. The RF signals that make up the RF beam are selected to create an emission pattern associated with object detection. Some of the RF antennas can be multi-purpose, where in addition to transmitting the RF beam, the antennas are used for RF communications. Upon receiving a reflected radiation pattern of the RF beam from an object, the reflected radiation pattern is analyzed to identify characteristics of the object. Depending upon what characteristics have been identified, one or more actions can be automatically performed.