They are many options out there when it comes to digital tools. The reality is none of them are perfect for focusing on safety.
NextDoor used to work really well but recently opened up the platform so it is really hard to get an alert just based on your block.
In fact when Neighborhood Watches are created, they often spend a ton of time trying to agree on a tool that will do the job of mass notification.
Existing Neighborhood Watches are sometimes stuck in the past, using paper and phone trees to communicate.
My personal experience was our watch group finally agreed to using a Facebook group, but it sort of died off after there wasn't a crime for a month or two. Neighbors weren't really engaged.
Then we decided to use a text messaging group which was hard to manage when a new neighbor moved in, and also hard to keep it focused on safety and security.
Finally, we started building Patrolio to solve this exact issue. It is not a social network. It is a digital neighborhood watch app that is really focused on safety and security. It allows you to define a private, very local block. It handles realtime notifications, including using text messages for the most critical information. Neighbors can easily post their videos, no matter what kind of cameras they have. Patrolio is not perfect but it is definitely one of the easiest way to setup and manage a neighborhood watch.