An IPAWS Wireless Emergency Alert (WEA) alert was received on a cell phone of a user located outside the polygon used by the notification.
IPAWS allows you to send Wireless Emergency Alerts (WEAs) to a polygon. When a WEA is sent, it hits the towers within the polygon and any tower whose signal reaches that polygon. This is one way someone outside the polygon can be alerted. Additionally, not all carriers and/or handsets currently comply with the 3.0 standard for reduced bleed over. This would be why some people within five miles received the alert. It is not uncommon for the bleed over to actually reach 25-30 miles. Five miles is common; not every carrier is in compliance with the 1/10 of one mile. This behavior is not controllable by Everbridge.
Have the citizen reach out to their carrier to follow up.
Note: In order to receive a WEA message, your handset must be WEA-capable, switched on, and in the vicinity of and receiving service from a cell tower of a wireless carrier that participates in WEA. Some participating carriers may offer WEA on some, but not all, of their mobile devices. Consumers should check with their wireless carriers to find out if their cell phone is WEA-capable.