Location-based warnings and mobile phone coverage
The Emergency Alert telephone warning system relies on telecommunications networks to send warning messages to mobile telephones.
Text messages can be sent based on the last known location of handsets at the time of the emergency. This includes visitors and people travelling in the area.
This diagram shows how the predicted coverage area of a mobile tower is used to identify which mobile telephones should be sent the warning message and, why you may receive a text message if you are outside the warning target area but you are nearby that area.
Selected target area to send warning message
Coverage into select target area
No coverage into select target area for warning message
Connection to mobile phone tower
Phone may receive warning message
Phone may not receive warning message