Android and iOS both seem to deliver localized emergency alerts such as weather warnings, amber alerts, etc. @quassy helped do some research on emergency alert APIs:

The Unites States NWS has this JSON API: https://www.weather.gov/documentation/services-web-api

It looks like we can request access to IPAWS alerts by sending an email: https://www.fema.gov/services-and-systems#

MissingKids.org has public REST endpoints http://www.missingkids.org/bin/ncmecEndpoint?endpoint=en_US&rest=&action=hashTables&languageCountry=en_US