A bullshit attachment that noobs use when playing Call Of Duty. In case you never played the game, it sticks out of your primary weapon and red dots flash on it when an opponent is near. When using a weapon with a heartbeat sensor attached, the user will usually camp in a corner of a room and watch it closely until someone comes close so they can easily kill their opponent. In my opinion, it is a more annoying attachment than the noob tube.
Stru: WTF! How the hell did he know I was there?! I didn't know it was possible to screen watch online!
Bryan: Nah, man. Calm your nuts. It was just another noob and his heartbeat sensor.