Anti-theft system for vehicles having remote-controlled engine starting function

When starting an engine (14) using its remote engine starter function in a guard mode, an engine control ECU (12) outputs an engine status signal at H level prior to driving a starter motor (13). An anti-theft control device (40), upon reception of the signal, stores the engine operating status in a mode storage device (50) and lower the detection sensitivity of sensors (25 and 26). This allows no false alarm to be generated, if the anti-theft system is initialized by the decreased voltage of battery at the time of driving the starter motor. In addition, the detection sensitivity of the sensors (25 and 26) is low until the engine (14) stops running, so that the sensors (25 and 26) do not have risks to erroneously detect the vibration of vehicle as an intruder.