A method for determining the presence of a transmitter and a receiver in a vehicle by means of a central processing unit, wherein said transmitter and receiver are designed for transmitting electromagnetic or optical signals in a predetermined direction and for receiving said signals from substantially the same predetermined direction, respectively, for example for communicating between different vehicles, and wherein said transmitter and receiver are operatively connected to the central processing unit, comprising the steps of: —generation of a signal in the central processing unit; —transmission of a signal by the transmitter in dependence on the signal generated in the central processing unit; —reception by the receiver of the signal from the transmitter; and —determination by the central processing unit of the presence of the transmitter and the receiver in dependence on the signal from the receiver.