node 12 enters it communication range and then switches back to the low duty cycle mode when the sensor node moves out of its communication range the present invention provides a method for a relay node 14 to wake its neighboring relay node up and initiate a seamless handover when detecting that the covered sensor node is going to move out of its communication range as shown in fig4 the relay node periodically evaluates the received signal strength indicator rssi values of the incoming data packets from the sensor node if a relay node 14 realizes that the rssi values decrease to a threshold or that the distance between the sensor node and the relay node derived from the rssi values exceeds a threshold the relay node will begin to send wake up messages to the neighboring relay node in the direction of the sensor node movement once the neighboring relay node wakes up it will stay in the active state then the current relay node initiates a seamless handover by sending messages to the neighboring relay node once the handover succeeds and the communications between the sensor node and the neighboring relay node is established the current relay node will go back to the low duty cycle mode.