The most widely used tracking tecnologies in present VE systems are mechanical, magnetic, acoustic, optical, and gyroscopic technologies. Mechanical trackers are very accurate and responsive, but they restrict the user's range of motion and aren't that good when it comes to multiple users.
Magnetic trackers are the most widely used of the technologies.
Acoustic Trackers use utrasonic frequencies. Acoustic tracking systems are primarily used in time of flight, time delay, and phase-coherent systems. Optical tracking systems are used in experimental VR systems, such as experimental ceiling trackers.