Someone has happened to him that during a game in sand the radar emits sounds and beats in a light yellow color
It's meant to be some kind of "distress beacon".
Then it is activated when a close friend is being hit?

I've been playing halo since it came out and I never had this happened, reviewing the video had only an invisible enemy within the radgo reach range
Yeah if you press up on the arrow pad it will do that. It was added a few updates ago as a way to communicate with your teammates without a mic, but I've never actually seen anyone use it.
If you press up on the D-pad, it'll give out a little ping for everyone on your team. They added it a while ago, seemed kinda pointless though and no one I ever play with knows about it.
Profesnol wrote:
If you press up on the D-pad, it'll give out a little ping for everyone on your team. They added it a while ago, seemed kinda pointless though and no one I ever play with knows about it.
It can be quite useful in firefight during those moments when you have no idea where the enemy has spawned.
Tapping up on the d-pad flashes your service tag above your head, alerting your teammates to your position. It can also be used as a crude form of communication.

It doesn't happen when you are taking enemy fire. It can only be done at the player's decision.
Profesnol wrote:
If you press up on the D-pad, it'll give out a little ping for everyone on your team. They added it a while ago, seemed kinda pointless though and no one I ever play with knows about it.
It can be quite useful in firefight during those moments when you have no idea where the enemy has spawned.
Yea but no one really knows about it, I do it all the time when I find a power weapon on the ground and I already have one of my own or when I need someone to come help me fight the enemy.

But no one ever comes because they don't know what it is.
It can be helpful in Infection too, when you find that one hidden camping survivor.
I've never been on the recieving end to go to a de stress call.

I don't know if it does any thing.
I find it very useful, they should add more of these skills, maybe something similar to pointing out objectives, so similar to the campaign
I agree need more of this skill as it's super useful