This is a continuation of a series about the three main types of alerting systems; subscription, opt-in, and mass/intrusive. The first article described subscription-based systems and the second opt-in-based systems.
A mass/intrusive system can be defined as one where the message is no longer targeted at individual subscribers, but rather to all people who may be within an area under threat. A recipient does not opt-in to receive the message, there is no contact list and hence there is no barrier to entry.
Examples of mass/intrusive systems are radio and television broadcasts, sirens, road signs, and Wireless Public Alerts (WEA in the US). A message is broadcast to all possible recipients within a given area in the hopes of reaching as many people as possible. The benefits of a mass system are that it reaches a much larger audience than subscription systems. There are no advance actions that recipients must take in order to receive the message, which significantly improves the uptake by the public.
There are some downsides to mass/intrusive systems. You are no longer targeting based on a list of users, but rather solely based on a threat area. That threat area may not be precise, or the distribution mediums may send the message outside the threat area because they cannot constrain their message solely by area (ex. radio broadcast). So the message may reach an unattended audience. There is also no reporting or feedback on the delivery of the message, what systems sent it out, how many people it reaches, etc. Finally, because recipients did not take any action to subscribe to, or receive, the message, they are not as prepared to receive the alert and recognize the authority of whoever issued it. The alert will catch them by surprise and proper steps must be taken to ensure a recipient can then validate the source and content of the message to confirm its authenticity.