An IMD (200) has its communication circuitry (270) in an inactive state and has access to two different identifier codes. The IMD (200) activates the communication circuitry (270) based on reception of a wakeup message (30, 40) comprising an identifier code that is identical to the identifier code currently assigned to the IMD (200). A communication device (100) generates and transmits first wakeup messages (40) comprising a first identifier code associated with the IMD (200) and second wakeup messages (30) comprising a second identifier code associated with the IMD (200). Depending on the currently assigned identifier code of the IMD (200) the IMD (200) will respond to either first or second wakeup messages (30, 40).
