A method for monitoring data processing and data transmission in a safety chain of a safety system (100, 200), wherein the safety system provides an overall safety function and is composed, in a modular manner, of at least two subsystem modules (110, 120, 130, 210, 220, 230), and wherein at least the two subsystem modules are connected to a data transfer channel and each provides a partial safety function and are configured for functionally safe data processing and/or data transmission, comprising the steps of: - processing data by a first one of the subsystem modules to obtain functionally safe data; - determining, by said first subsystem module, a first actual characteristic value for a safety-relevant characterizing attribute of the data processing and/or data transmission, in particular for a total response time; - transmitting the functionally safe data and the first actual characteristic value from said first subsystem module to a second one of the subsystem modules, and receiving the functionally safe data and the first actual characteristic value by said second subsystem module; - determining, by said second subsystem module, a second actual characteristic value for the safety-relevant characterizing attribute; - processing the first actual characteristic value and the second actual characteristic value so as to obtain a third actual characteristic value for the safety-relevant characterizing attribute, by said second subsystem module; - determining, by said second subsystem module, a nominal characteristic value for the safety-relevant characterizing attribute; - comparing said third actual characteristic value with the nominal characteristic value of the safety-relevant characterizing attribute, by said second subsystem module, and, depending on the comparison result, - if the result of the comparison is positive, further processing and/or forwarding the functionally safe data; or - if the result of the comparison is negative, triggering a predefined safety reaction. - processing data by a first one of the subsystem modules to obtain functionally safe data; - determining, by said first subsystem module, a first actual characteristic value for a safety-relevant characterizing attribute of the data processing and/or data transmission, in particular for a total response time; - transmitting the functionally safe data and the first actual characteristic value from said first subsystem module to a second one of the subsystem modules, and receiving the functionally safe data and the first actual characteristic value by said second subsystem module; - determining, by said second subsystem module, a second actual characteristic value for the safety-relevant characterizing attribute; - processing the first actual characteristic value and the second actual characteristic value so as to obtain a third actual characteristic value for the safety-relevant characterizing attribute, by said second subsystem module; - determining, by said second subsystem module, a nominal characteristic value for the safety-relevant characterizing attribute; - comparing said third actual characteristic value with the nominal characteristic value of the safety-relevant characterizing attribute, by said second subsystem module, and, depending on the comparison result, - if the result of the comparison is positive, further processing and/or forwarding the functionally safe data; or - if the result of the comparison is negative, triggering a predefined safety reaction. - if the result of the comparison is positive, further processing and/or forwarding the functionally safe data; or - if the result of the comparison is negative, triggering a predefined safety reaction.