Immobilizer with a short release time

The invention concerns an immobilization device for vehicles having a control apparatus (10, 12, 15) which is isolated only when an authorization check has been carried out. A preliminary release arrangement (19) unconditionally releases the control apparatus (10, 12, 15) on starting for a preliminary release time (Tvor). According to the invention, the preliminary release arrangement (19) restricts the number of possible successive starts with unconditional release to a value which is predetermined in each case. This value is smaller than the value last set if the preceding start was irregular.