Staged rollout with engagement metrics that cancel the alert if it’s not alerty enough.

Stages: one town, then a city, then one county, then everyone. Can be complemented by picking a percentage nationally as well, or picking two different towns (Croydon vs Barnstaple.)

Engagement: Poll at each stage as to whether the message was useful, or counted as an emergency, or was read for more than X seconds, or opened more than once.

The alert system also has four levels:

(1) National and (2) Imminent Threat (think “we interrupt this programme to bring you breaking news…”);

(3) Public Safety (“Charlie says” but more specific); and

(4) missing persons / Amber alerts.

The use of the we’d-rather-you-crash-your-car-than-not-get-your-attention klaxon should be reserved for the first two, and its use for the “no barbecues plz” warning should probably have been avoided.