From [my related question](https://aviation.stackexchange.com/questions/17693/do-fighter-jets-have-forward-looking-radar-warnings-for-missiles-and-when-was-t/17696?noredirect=1#comment42945_17696), it seems fighter jets do not usually track missiles by radar. Instead, they have a system that warns of radar lock.

So what about infrared missiles (heat-seeking missiles)? Flares are a countermeasure to these, so how does the jet know when one is incoming?

I would be pretty surprised if such a system didn't exist. I want to know more about that system and when it was first implemented.