Unscheduled wireless communication with a medical device is achieved by operating a receiver of the medical device in a series of modes. Each mode provides an increasingly selective evaluation of received RF energy. The receiver, when operating in a first mode, is capable of detecting the presence of RF energy transmitted from a communicating device. The receiver, when operating in a second mode, consumes more energy than the first mode and analyzes the RF energy to determine whether it contains the appropriate type of modulation. When operating in a third mode, the receiver consumes more energy than the second mode, and operates the full receiver to begin communication with the communicating device. The receiver opens a communication session after the RF energy has passed the evaluation by the series of modes to receive an unscheduled communication.