A method for detecting faults during transport of a web in a web-fed printing machine, wherein web speed is determined by contact-free measurement, in accordance with the Doppler principle, includes the steps of: by applying microwaves, determining a first local speed of the web at a first measurement position; by applying microwaves, determining at least a second local speed of the web at a second measurement position spaced apart from the first measurement position in a direction of web transport; determining an actual value from the first local speed and at least the second local speed; determining any deviation of the actual value from a predefined desired value; and comparing the deviation of the actual value from the predefined desired value with a predefined threshold; a detecting device for performing the method; and a printing machine including the detecting device.