The invention is directed to an apparatus for triggering passenger protection systems particularly restraining systems in vehicles during their impact. In the previous systems, there is the disadvantage that the protective systems are only triggered late or not at all during critical impact situations at relatively low negative accelerations. The disadvantage chiefly results because a differential signal is fed to the input of an integrator which comprises the difference between a signal derived from the acceleration and a constant threshold value signal. According to the invention, a variable threshold value is deducted from the derived acceleration signal rather than a constant threshold value.