In a method for activating a destination network node (SN) to be woken up in a wireless network (1), in particular a sensor network, the destination network node (SN) is woken from a sleep operating mode if the destination network node verifies a received secret wake-up token (WUT) by a predefined test function and at least one stored wake-up token reference value (WUTRV). The method protects network nodes in a wireless network (1) from attacks which reduce the lifetime of the network nodes by preventing a sleep operating mode. The method is particularly suitable for sensor networks.