Begin
Switch the working mode of sensor do
Case  sleeping mode
   If timer is up then
    Change to monitoring mode;
   Else If get activation message then
      Change to monitoring mode;
    Else wait;
Case  monitoring mode
   Detecting target;
   If target detected  then
    Broadcast “wake” message to one hop neighbour;
    Change to target mode;
   Else
    Change to sleeping mode until receive “sleep” message;
Case  target mode
   If the closest node then
    Broadcast “wake” message to one hop neighbour;
    Tracking target;
   Else
    Tracking target;
   If target disappear then
    Broadcast “sleep” message to one hop neighbour;
    Change sleeping mode;
End
Algorithm 2: Working mode of nodes.