Sharing warnings about unusual dangers always has been a basic function of any community. As governments' ability to detect and forecast hazards has grown, so has the expectation that public officials will provide swift and effective warnings to their residents.

Fortunately, the insight gained from the study of public warning has combined with technological advancements to produce some much-needed help in sorting out public warning options. Two of the most basic of those research-based insights reveal the importance of relevance and corroboration.

Relevance is a more precise way of discussing the “cry-wolf syndrome.” In reality, the public is remarkably tolerant of false alarms as long as they were issued in good faith and when they are not so frequent as to suggest negligence. But, people do not tolerate irrelevant warnings — those that do not apply to them. So, the ability to target warnings precisely to the area at risk is a major advantage of geographically targeted telephone notification systems over broadcast-based systems like the Emergency Alert System (EAS), which requires TV and radio broadcasters to issue emergency government warning messages.

Also, people rarely act on a single warning message; at best, they start to pay attention and look for corroboration. Typically, people must receive the information from several different sources — warning systems, friends or family, direct observation — before they try to avoid danger.

So, effective warnings need to be delivered simultaneously and consistently by a variety of methods. That means public safety agencies need a way to control multiple warning systems to spread consistent messages without overburdening their personnel.

In the last few years, a group of more than 130 emergency management practitioners, technologists and academic experts developed the Common Alerting Protocol (CAP), a non-proprietary international data standard, to help coordinate and control multiple warning technologies. Federal authorities and a number of states and local jurisdictions are using CAP to control sirens, telephone notification systems, EAS and Weather Radio broadcasts and a variety of other public warning technologies.

A single CAP alert message, created by a variety of stand-alone programs and emergency management software packages, can activate and control any CAP-compliant warning delivery system. CAP's digital format simplifies warning delivery to people with disabilities, such as the hearing-impaired. It also helps communicate the warnings in multiple languages (although it does not solve the problem of creating useful and specific warnings in the wide array of languages).

Public warning is no longer an ancillary duty of particular departments or a specialized response to specific hazards. An integrated all-hazard approach to public warning, based on scientific research into “warnings that work,” can deliver the service better, faster and cheaper.

The author is community warning system manager for the Contra Costa County, Calif., Sheriff's Office.