A method for protection against a relay attack on a system is composed of at least a first and a second communication device. Data are transmitted wirelessly between the first and the second communication device. The first communication device ascertains a first spectrum of all wirelessly transmitted signals to be received at the location of the first communication device within a frequency band. The second communication device likewise ascertains a second spectrum of all wirelessly transmitted signals to be received at the location of the second communication device within the frequency band. The frequency band is limited by a minimum and a maximum frequency. The second communication device transmits the second spectrum to the first communication device. The first communication device compares the first spectrum with the second spectrum in order to ascertain whether the second communication device is located at the location of the first communication device.