The rifle beeps so you can't hide in one place and shoot without being heard or seen, the beep allows the other player to detect you by audio if you are not seen
I just got this for my son's bday. He & his sister tried them out to check they work (because the 1st set arrived broken). I had to wrestle them off them after like 30 mins to hide them away til his bday 😂 They thought they were inside Call Of Duty!