… messages by county or equivalent jurisdiction might be too coarse-grained, especially in the case of large counties and highly localized events.”2 Past research has shown that specific and clear information, including which locations are and are not at risk, increases the likelihood that people take protective action. The less precise the geotargeting, the more likely the recipient will ignore the alert, or choose to opt out of the alerting system, because they are not sure whether the message applies to them. When alerts and warnings are delivered to broader populations than those actually affected by an event, more people than are actually at risk may be sent messages to take action. This chapter explores discussions held by panel members and attendees of the February 2013 workshop on public response to geotargeted alerts and warnings.

There are several systems that provide geotargeted alerts today, with various degrees of precision. Some, such as the so-called “reverse-911” systems, can dial groups of landline telephone subscribers and can achieve a high degree of precision because they are capable of calling subscribers located within a specific polygon. On the other hand, wireless-based systems, such as the Emergency Alert System (EAS), are inherently less precise because of the wireless fencing issue. In the case of the national Wireless Emergency Alerts (WEA) system, alerts are transmitted to cellular phones using cellular broadcast technology.3 Only cellular mapped to the geo-defined region broadcast the message. However, the geotargeting precision of WEA in its initial rollout was additionally affected by a design decision to limit geo-definition to the county level. Another system is the National Oceanic and Atmospheric Administration (NOAA) weather radio, which uses dedicated radio frequencies and special-purpose receivers. It delivers weather and other hazard alerts and allows users to limit alarms to only those alerts designated for their location by specifying regions that are largely aligned with counties or portions of counties. Other services allow recipients to subscribe to alerts for geographic areas of interest to them, regardless of their actual physical location. Generally, such systems are not considered to possess true geotargeting capability.

Better localization might be provided by refinements to existing alerting systems or the use of new technologies. For example, some tighter localization is possible with the current WEA technology, but overlaps in coverage of individual cellular towers limit the precision that is possible. Additionally, if alert messages include information about the target


2 National Research Council, Public Response to Alerts and Warnings on Mobile Devices: Summary of a Workshop on Current Knowledge and Research Gaps, The National Academies Press, Washington, D.C., 2011.

3 WEA was formerly known as the Commercial Mobile Alerting System.

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