The disclosure relates generally to wireless communication with an implantable medical device. An implantable medical device (IMD) may initiate the establishment of a communication session by sending a wakeup communication to an external device with which the IMD desires to communicate. The external device may operate in low power state (sometimes referred to as a sleep state or a low current state) in which the external device occasionally powers up telemetry circuitry to monitor for the wakeup communication from the IMD. Upon receiving the wakeup communication, the external device transitions from the low power state to a high power state to establish the communication session with the IMD. Operating the external device in the low power state when no communication session is established reduces the amount of power consumed by the external device when no telemetry is occurring, thus enabling the external device to be powered by a battery.
