The Sensors mark where there are Papoo Wave events. These Wave events have a number of papoo that spawn. They consists of 5 waves where the mobs will get higher in maturity. And the last wave with consists of a King. The King has been know to loot time travel crystals :) Each of the papoo waves usually consists of 20 mobs. EXCEPTION: The Grey papoo waves will have 100's (some have said 600, but I think that number is a bit exaggerated) :) Sensor Alpha: Crystal Center Sensor Beta: 136959-84080 Yellow Papoo Sensor Delta: 136203-84011 Red Papoo Sensor Gamma: 136113-84827 Brown Papoo The Grey Papoo wave is at: 136905-83422, but there is no Sensor there. Also if you complete all 5 waves for each papoo area you are awarded with a Papoo Slayer Achievement. Take out the Apes! :)
Actually the whole grey pappoo wave event (all 5 waves) has more than 500 mobs, since both me and Buzz were done our mission and the event was not over yet. So no, its not exaggerated.