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Achtung baby! Design tips for alarms, alerts, and warnings

Back in the 90s when I was a free-healed, adventurous young man, many a rock climbing outing was set to the sound track of the Irish rock band U2. Eventually, the title of one of their popular albums became the sounding alert of any hazard my companions and I faced. Whether a rattlesnake on the trail, a long unprotected stretch of vertical rock, or a loose boulder on the descent, “Achtung baby!” was shouted out in warning.

This playful call to attention was usually sufficient for a couple of guys in the wilderness, but in the often high stakes environment of today’s technological (and often highly automated) world, the design of alerts and warnings requires some thoughtful consideration.

Although the terms alert, warning, and alarm are often used interchangeably, they can be differentiated by the level of urgency required in response. Alerts are generally described as an information display generated when awareness is needed and some information must be conveyed concerning a non-normal event or situation that may or may not require action. Warnings describe a display relating to a critical condition requiring immediate awareness and immediate corrective action. An alarm is often understood as a display indicating that some condition exists that will require human action to correct to prevent loss of life, property, or equipment. For simplicity sake, I will refer to all three as “alerts”.

Effective alerts need to be readily detectable, easily heard and seen under all ambient noise and light conditions, able to be correctly interpreted, and able to minimize errors that could create additional hazards. Here are a few additional tips for designing successful and effective alerts and warnings.

• Eliminate confusion

Eliminate the possible confusion of alerts with any other displayed information by creating differentiating features with the use of color coding, sounds, and tones. Ensure that visual alerts are labeled so that they are legible and understandable. When possible, place the most critical visual displays in the operator’s primary field of view. If many alerts are required, consider the use of a central location or panel where visual warnings can be easily seen and identified. To ensure that audible alerts are easily recognized and understood, each alert sound should have only one meaning.

• Provide information

To minimize the time required for the user to detect and respond to the problem, symbology and coding can provide the operator with useful cues to the needed response. Spoken alerts can have advantages over other forms of auditory warnings because they can provide specific information without the user having to interpret a tone. Text displays can offer further information such as “right engine on fire” or “blood pressure low”, or even suggested actions, such as “exit car immediately”.

• Match intensity with criticality

The intensity of an alert needs to be matched with how serious the situation is and with the urgency that the user must respond. In the most critical situations visual alerts should be displayed until the user has responded or until the hazardous situation no longer exists. Auditory or voice alerts should accompany high priority alarms. Lower criticality alerts should be less intrusive to avoid becoming annoying or unnecessarily increase operator workload. All auditory alerts should be of moderate intensity to avoid startle or panic responses that will disrupt performance or lead to mistakes.

• Create trust

If an alert is displayed too frequently, the user may stop seeing or hearing it, or even worse begin to intentionally ignore it. This will cause the user to distrust the warning and essentially render it ineffective. To avoid the loss of user trust, make alerts appear and repeat only when necessary, at appropriate intervals, and only as intrusively as the criticality of situation requires. Minimizing false alarms is critical to maintaining user trust. Some systems may allow the user to interact with the displayed alert by cancelling it and acting accordingly, or by selecting a choice from a menu. Interaction of this kind gives the user a sense of control that can help to maintain trust. A system test feature that verifies that all alarms are functional can also help the operator feel confident that seldom heard or seen alerting systems are reliable.

For detailed information on human factors considerations for the design of alerts, warnings, and alarms, and in the specific application to flight deck components, check out the HFYI Design CoPilot™ at http// A product of Research Integrations, HFYI Design CoPilot™ lists 14 human factors considerations for alerts, warnings, and alarms regarding controls, displays, systems and testing assumptions. It also provides information from FAA regulations and guidance materials, as well as industry standards documents from ARINC, RTCA, SAE, and GAMA.

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