There is only reaction by capacitive (capacitive) proximity switch acting on the lock (lock) in the door in this case two conditions grip (grip) area of ​​the vehicle door is arranged to be met. The first condition is that the data communication between the portable transmitter is authorized persons and ID- ID- receiver which is fixed in the vehicle in possession be made smoothly. Another condition is detected by the sensor in response to the incoming object in the action range of the proximity switch. However, the sensor acts on the lock only when the variation rate of capacitance is more than a set limit value. In order to prevent unnecessary discharge of a car battery, a method for providing different two capacitance change rate limit value, which is controlled by the determination as an alternative group (discriminator) it is proposed. Discriminator mutually and counter to determine the count rate per unit time by measuring the action capacitance variation time count. Average speed is only valid lower limit. However, if the counting rate exceeds a prescribed threshold, it determines group activates the upper limit speed.