This morning I read that mulitple people got (light) physical injuries after a passenger flight had to forcefully drop its altitude quickly in order to avoid collision with a fighter jet. The news article stated that it was flying at a "safe" distance of 1,000 metres for a visual inspection, and that there was no danger at all. Although some other sources state that the distance was only down to a hundred meters
To me (someone who knows next to nothing about flying) a distance of one kilometer sounds pretty close for two planes to fly at (seeing the speeds planes travel at). The article states that this is "in accordance with international standards", but from this answer I understood that 3 to 5 miles (4.8 to 8km) is the general distance. However that answer also states that in a "Military Operations Area" this may not be the case (which this area might have been in, but then I feel like it wouldn't have mattered that it was "in accordance with international standards", as those don't apply then anyway).
That said, are there any alarms or warnings that start going off when another aircraft gets so close to warn the pilot of possible collision, or is a pilot trained to undertake action based on what his/her visuals/flight data are telling him/her at the moment? (I have read before that measuring a distance by visuals is very hard in open air due to there being no reference points, so I think it is unlikely that a pilot would act up on that alone). What is the protocol for a pilot suspecting the possibility of a mid-air collision?
It seems that this incident is also a bit of a political issue. I am not trying to discuss if everyone took the right actions here, and what the intentions of the parties were. Just interested in the protocol behind making such a drop.