ACA Allertor 125

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The ACA Allertor 125 is an outdoor warning siren made by American Signal Corporation (formerly Allerting Communicators of America and Biersach & Niedermeyer Co.) from 1944 until 1980. It has a distinctive design with the chopper in the bottom horn and the noise coming out of the top horn.

Watch an ACA Allertor 125 in alert and attack.


The ACA Allertor was originally designed in the early 1940s as the B&N (Biersach & Niedermeyer Co.) Mobil Directo and was used for air raid warnings during World War II. The Mobil Directo was made of metal. It came in 4 different port ratios. 8, 8/12, 9/12, and 10/12, with 9/12 being the most common. The siren could reach up to 125db, hence the name "ACA Allertor 125". The single tone 8, dual tone 9/12 and dual tone 10/12 rotors were derived from Federal Signal Corporation. In 1968, during the height of the cold war, B&N changed their name to ACA (Allerting Communicators of America) and changed the Mobil Directo to the Allertor. Many designs were changed, such as the Mobil Directo having an exposed motor and a belt-driven rotator, and the Allertor having a covered motor and a chain-driven rotator. During the early 1970s, the Allertor was changed from metal to fiberglass and the bottom horn was made larger to reduce snow intake to the rotor. The ACA Allertor was a popular choice for a warning siren in the Midwest during the 1960s and 1970s. The siren was mainly used for air raid warnings (during the Cold War) and weather warnings (after the Cold War). The ACA Allertor 125's production stopped around 1980, when it as replaced with the more efficiently designed Penetrator 10. Unfortunately, these sirens are becoming more uncommon due to their age and because of newer technology.


The ACA Allertor 125 had a unique design, using the bottom horn as the air intake, and the top one as where the noise mainly came out. The air would first be sucked into the bottom horn, then into the donut-shaped metal sphere, where the chopper was located. The chopper would then make the sound and blow it out through the top horn. The siren could be heard from several miles away on a clear day. Unfortunately, the siren's size could prove to be quite difficult, as strong winds could blow it down. Also, the chain-driven rotators sometimes broke, usually leading to their failure, removal or downright replacement.

Cities with ACA Allertors[edit]

Manhattan, Kansas

and many more.