A communication circuit of an implantable device is coupled to a power source (e.g., including a battery) upon receipt of a radiofrequency (RF) signal at the implantable device. A circuit that controls whether the communication circuit is to be coupled to the power source obtains its power from the received RF signal. Thus, the implantable device is able to perform RF signal monitoring (e.g., RF "sniffing") without using battery power. Battery power is then used for subsequent communication operations after it has been determined that the implantable device is receiving RF signals (e.g., from a verified external device).
