On April 18, 1775, Paul Revere (and other riders) went on his famous 'Midnight Ride' to warn fellow colonists that the 'regulars' were coming to seize their weaponry and arrest their rebel leaders.
When technology is unreliable, unavailable, or risky-to-use, well-connected networks of well-connected people (you may not agree with his theory, but see Malcolm Gladwell's 'Tipping Point' for more on the importance of selecting well-connected people) have, for hundreds (thousands?) of years, been utilized to sound alarm.
Is there a way to utilize (and improve or augment?) this old tool?