Editing Civil defense siren (section)

==== Basic design ====
[[File:ACA Allertor 125 video.ogv|thumb|left|175px|An ACA Allertor 125 in Alert and Attack modes (video)]]
[[File:3T22 Sandy, Oregon.jpg|thumb|left|175px|An older and damaged 3T22 at a fire station in Sandy, Oregon, that has now been restored and hung from the ceiling of the entrance lobby]]
[[File:IsraeliAirRaidSiren.jpg|thumb|left|175px|A Hormann HLS F-71 Pneumatic air-raid siren in [[Haifa]], Israel. Sirens of this type are common in Israeli towns and cities, and until 2012<ref>{{Cite news|last=זיתון|first=יואב|date=2012-02-20|title=שקל אחד, וכל הצופרים הישנים יורדים מהגגות|language=he|work=Ynet|url=https://www.ynet.co.il/articles/0,7340,L-4192091,00.html|access-date=2023-10-08}}</ref> were used to warn against air raids and missile attacks.]]

A mechanical siren uses a [[Rotor (electric)|rotor]] and [[stator]] to chop an air stream, which is forced through the siren by radial [[wikt:vane|vane]]s in the spinning rotor. An example of this type of siren is the Federal Signal 2T22, which was originally developed during the [[Cold War]] and produced from the early 1950s to the late 1980s. This particular design employs dual rotors and stators to sound each pitch. Because the sound power output of this type of siren is the same in every direction at all times, it is described as omnidirectional. The Federal Signal 2T22 was also marketed in a three-signal configuration known as the [[Federal Signal 3T22]], with the capability for a ''high–low'' signal.<ref>{{Cite web|title=2T22 and 3T22|url=https://wiki.airraidsirens.net/2T22_and_3T22|access-date=2021-10-08|website=Air Raid Sirens Wiki|language=en}}</ref> 

While some mechanical sirens produce sound in all directions simultaneously, other designs produce sound in only one direction, while employing a rotator mechanism to turn the siren head through 360 degrees of rotation. One rare type of mechanical siren, the Federal Signal RSH-10 ("Thunderbeam"), does not rotate or produce equal sound output in all directions. It instead uses a slowly rotating angled disc below the siren which directs the siren's output throughout 360 degrees.<ref>{{Cite web|url=https://wiki.thesirenboard.com/RSH-10|title=RSH-10}}</ref>