Forum:Ninja (not pro)

Hey guys, I'm new to this type of forum, so tell me if I'm doing anything wrong please... Okay, so my question here is about the effects of the ninja perk. Without pro, the purpose of the perk is to be hidden from heartbeat sensors right? Well when I'm playing, it seems as if it doesn't work, does anyone else have this problem? I was running around once, trying to find guys, and I was just about to kill some guy when he just by chance turns around to look at me. I check out the killcam, and right there on the heartbeat sensor, is a red dot, representing me. And when you look at the killcam, there isn't an ally there either. If anyone has any information on this, please help!!