Fri Nov 17, 2006 9:48 pm
Fedelcode sirens had brakes and shutters so that the siren signal could be controlled in bursts of sound. This way a coded signal could be sent out, like Box 5-2-3. In the days before widespread radio, this is how volunteers would know where to go, since a city would be divided up into boxes for every pull box, street corner, or major occupancy, etc. Some cities, like New York, still use the box system for locations. One World Trade Center was Box 8-0-8-7, and Number Two was 9-9-9-8.