Yes, it is possible to know if you are hooked by a speed camera. This is done by analyzing the radar signals emitted by the plane that is hooking you. An aircraft’s radar that detects you has several modes of operation, including scanning (for detection) and tracking.
When scanning, the aircraft tries to spot targets everywhere around it, and therefore sends out radio waves in all directions while scanning. The target aircraft therefore receives an intermittent signal from this radar. During lock-on (tracking), the radar “tracks” the target by constantly sending a signal in the direction of the target. The target aircraft can therefore make the difference between the two, and signal to the pilot that he is indeed targeted by a radar. On the other hand, by analyzing the signal itself, it is possible to know, for example, whether a radar-guided missile has just been launched, because the signal emitted by the radar is different.
All this information is provided to the pilot by the RWR (radar warning receiver), which also makes it possible to know where the radar signal in question comes from.
To make a more concrete analogy, imagine that you are in the middle of the night, and that a tower with a very powerful searchlight is looking for you. In “scan” mode, the people on the tower would point the searchlight in all directions to try to find you, because they don’t know where you are a priori. If you’re far away, you’ll see the light from the tower long before anyone on the tower can see you, because you reflect little energy. If you get close to the tower, there will come a time when you can be detected when you are in the searchlight beam. This is the detection threshold. It depends on your “stealth”. If you look like a giant disco ball (that would be the equivalent of a large non-stealth aircraft like an AWACS), you’ll be seen from far away.
As soon as you are detected, the spotlight will constantly be trained on you, even if you try to move to escape the spotlight beam. This is the “pursuit” mode. This is how you can tell if you are “hooked” or not.
Note two things
- this principle works for other vehicles (boats, submarines, etc). If you read the book “Red Storm” by Tom Clancy, there is a scene where the US submarine is near the Soviet coast, and where it detects enemy coastal radars in a periscopic dive. It advances towards the coast and dives again before approaching the radar detection threshold, in order to remain invisible.
- On the other hand, it is impossible to know if you are hooked by an infrared system. because these systems do not emit anything (they simply analyze the infrared radiation emitted by the engines). However, you can still detect the launch of a missile (which itself has an infrared signature due to its rocket engine), even if you cannot know a priori who it is aimed at.