BP Exploration undertook the development of a new rig safety system to provide an increased level of protection against sub-surface well collisions. The Watchdog system is an acoustic wellhead monitoring system designed to warn the driller when a collision with an existing well is imminent. Monitors are placed on the wellhead of each well considered an intersection risk to detect vibrations created by an approaching drill bit. This data is processed in real time and plotted versus measured depth of the well being drilled. By this means the approach of a drill bit can be detected before impact occurs and correctional action may be taken to avoid collision.