"Terror Radius" also known as "The Heartbeat" is a in-game sound effect that can only be heard by the Survivors, who are within a certain distance of the Killers while The Terror Radius is set at a range of 32 metres, this range could and can always change depending on the chosen Killers that or adding Perks. But this "Heartbeat" is not of the killers it is the chosen survivors which will give them a enhanced method of escaping before a Killer has arrived at their location.