From the NYC Disaster Interfaiths Service which is worth considering elsewhere in the U.S.

NYC HOWalert (House of Worship Alert System) – 2000 Subscribers and Growing. Launched in April 2017, In partnership with the NYC Faith Sector Community Preparedness Program Advisory Board, NYDIS is now providing HOWalert, a free emergency notification system for all NYC religious leaders. Only used during emergencies and two optional annual tests/exercises, HOWalert sents emergency information to registrants by text, email or voice messages. That message will notify NYC religious leaders and other Faith Sector communications decision makers, about life threatening or urgent crisis management incidents that should be rapidly shared with their congregants, clients or staff – or, that may impact their facilities and programs. The system may also be used for two-way communication – to send a message and then collect damage assessments or to allow religious leaders to submit requests for help during an unfolding public health emergency or disaster. All information submitted is kept STRICTLY CONFIDENTIAL.

Because NYDIS receives and distributes Crisis and Risk Communications (CERC) from government and the non-profit (VOAD) sectors, our staff take the time to adapt the information for a faith-based context – addressing how the incident may affect worship and public gatherings. As well as how and what congregants, clients or staff should be informed of the threat and what they should be told to do. Religious Leaders are often critical transmitting trustworthy life saving information.

Any faith-based organization or religious body in NYC may submit their contact lists for bulk upload, and then use HOWalert to send their own messages at their discretion, free of charge.