In this paper, we develop a formalism describing in a relativistic way a system which consists of a classical and a quantum part which are coupled. The formalism models one particle with spin 1/2 and it is a possible relativistic extension of the event-enhanced quantum theory. We postulate a covariant algorithm which plays the role of the standard reduction postulate in non-relativistic quantum mechanics. Furthermore, we present an algorithm to simulate detections of the particle.