This chapter summarizes a long-established psychological model that can provide deep insight into how people detect ‘weak signals’ that something might be wrong with an operation or process, and how they decide whether or not to intervene when they do detect such weak signals. The chapter illustrates the role that good implementation of HFE in design can play in making it easier to detect and recognize the significance of ‘weak signals’. Organizational and cultural factors will dominate an individuals willingness to take action if they do detect weak signals of trouble. But HFE has an important role to play in making weak signals stronger by design, as well as ensuring that signals that should be ‘strong’ and easy to detect are not made weak by the design of the work environment and equipment interfaces.