Two or more transceiver units can interact with each other via millimeter wave radio frequency signals. One of the transceiver units can detect time-varying signals having specific waveforms in order to initiate an action such as establishment of a communication link, powering a piece of equipment and the like. The time-varying signal can be generated by a user moving one of the transceiver units and/or by passing an non-transmissive obstruction in between the transceiver units. Related apparatus, systems, and methods are also disclosed.