Category:Coded Sirens

While no longer used today, coded signal blasts were once commonplace in large cities as a way to direct firefighters towards a fire. Cities would be split into various districts or zones, each with its own assigned number. Call boxes would be placed around each district, and when used, would cause the fire station's siren to activate and blast the same number of times as the district's number. This made it clear where the fire was located without radios or other forms of communication, no doubt saving lives with the time this saved. The sirens themselves could be a basic two-signal siren simply wailing a certain number of times, but some stations used coded sirens, which are in this category.

Coded sirens use a brake or a damper in order to rapidly bring the siren to a halt, or choke off its intake to silence it quickly. This achieved quick coded blasts that were distinct from a normal siren, and were reminiscent of the fire bells, whistles and horns large stations used before sirens were common. Coded blasts were also faster than a wailing siren, with some sirens such as the Fedelcode Model 2 being reported to even be able to send Morse code. As every second counts in an emergency, this proved very useful.

With the advent of personal radios and dispatch, the need for coded sirens rapidly diminished. The location of fires could be shared far faster over the radio than with a siren, and far more precisely. The brakes and dampers on coded sirens required significantly more maintenance than a normal siren, as they would freeze up if not used or maintained regularly. As such, most stations would replace their coded sirens with standard electric sirens or pagers. Others would keep their code sirens, but run them as a standard siren.

Note: Coded sirens and three-signal sirens are two different things. Coded sirens specifically mean sirens that were primarily designed to produce coded blasts for firefighting use and similar purposes, instead of having a third signal to use. Three-signal sirens are simply two-signal sirens with added dampers or solenoids that are primarily meant to produce a third signal for when more than the standard steady and wail signals is required, or a different signal is preferred. Three-signal sirens are typically used at fire stations to summon the firefighters to the station with a distinct signal.