Transverse vibrations of a semi-bounded string consisting of different materials are considered. The homogeneous wave equation with piecewise constant coefficients stand duty as a mathematical model. As a first step, we have investigated the solution of this equation with zero Cauchy data. The existence and uniqueness of the generalized solution of the problem were proved and the properties of the solution were analyzed. The specificity of the obtained conclusions was discussed, in particular, the zones of oscillations’ propagation and of their absence were demonstrated. The obtained results are of a constructive character and can serve as a basis for the creation of a numerical algorithm. The importance of such problems is caused by their use in the theory of sensing inhomogeneous media by physical signals.