In the aftermath of some high profile national security incidents, investigations starting with the catastrophe or near miss and working backward have shown a clear series of events or warning signs which if recognised may have allowed the incident to be prevented. The security services have subsequently been criticised for being unable to connect the dots and intervene appropriately. Similarly, investigations into process safety incidents that work backward from the loss of containment or other more serious outcome often show a clear series of events or warning signs which if recognised and acted upon may have prevented the incident. In the build-up to both security and process safety events; however, the pattern that is so clear after the fact is often obscured or perhaps unrecognisable due to the other activities that are happening and all of the extraneous information that is available at the same time. In process safety, control room alarms often fall into the category of important information that is visible after the fact but missed or obscured leading up to the event. There are two broad approaches for improving the effectiveness of alarms. The first is to reduce the extraneous information for the operator by reducing the total number of alarms or addressing the rate at which alarms come in during a plant upset. The second approach is to improve the visibility of the alarm and ensure clear expectations for response for the most important or critical alarms. This article focuses on the latter and outlines principles for improving the effectiveness of critical alarms, defined here as those where the alarm and the expected operator response are considered to be a layer of protection against a major accident hazard scenario. These principles include aspects of the process design, ergonomics and the human machine interface, training, safety culture, and auditing. In an operating company, responsibility for these elements and the associated work processes are often owned by different parts of the organisation. It is therefore important that the management systems and organisational structure provide strong linkages to ensure the different work processes or departments mesh effectively to deliver a robust alarm system and associated operating discipline. (c) 2013 American Institute of Chemical Engineers Process Saf Prog 32: 6671, 2013