Android does, and I haven't had reason to disable it yet. Should that be necessary, people can leave a message. They might have to, even if they were whitelisted as I don't take my phone with me to the bathroom or to most meetings.

If "something" happens, by the time the police are contacting you it's no longer an emergency.

Responding to an ambiguous worry of an emergency that may never even occur during your lifetime by allowing yourself to be continually interrupted by spammers (traditional call-based and new app-based) is actually a decent illustration of the overarching societal problem.