The invention relates to a vehicle security system in the form of a keyless-go system and an operating method for it. In the vehicle security system, incorrect detection of a position of an authentication element (1) inside or outside the vehicle by authentication element locating means (21) in a vehicle-mounted access control component owing to at least one interference transmitter (10) which is present in the surroundings of the vehicle and/or of the authentication element (1) is avoided by using a device for performing empty measurement (9) in the authentication element (1). To do this, the device for performing empty measurement (9) performs a measurement in time periods in which the vehicle-mounted access control component (2) does not emit any pulses to the authentication element (1), by means of which measurement the interference level caused by the at least one interference transmitter (10) is determined. Depending on whether this determined interference level exceeds or drops below a predetermined threshold value, either the device for performing empty measurement (9) transmits, to the vehicle-mounted access control component (2), an adapted threshold value for a decision as to whether an authentication element (1) is located in the vehicle or outside the vehicle, or said device does not respond to subsequent pulses from the vehicle-mounted access control component (2).