The Allertor 125 was a rotational, electromechanical civil defense siren that was produced by Alerting Communicators of America from 1968 until it was replaced by the similar Penetrator series in 1980. The Allertor was the direct successor to Biersach and Niedermeyer's Mobil Directo siren, with significant improvements to the design. It is unique in that it sucks in air through the bottom intake horn, and then the sound comes out of the top horn of the projector.
The Allertor 125 used a 10HP motor, with 15 also being offered. Sound output was rated at 126 dB at 100ft. Rather than using metal, ACA used fibreglass construction on these sirens, which greatly improved the siren's longevity and durability as it prevented corrosion. The siren was rotated as one large unit, with the siren's motor being connected to a gear reducer that then drove a gear-driven or chain-driven rotator below. This design was quite reliable, as chains are far more durable than belts. A popular misconception is that the Allertor's chains were prone to snapping, but this is far from the truth. Allertors were and still are very reliable sirens. The Allertor came in three different generations:
Generation 1: The Gen-1 Allertor is easily distinguished by its elongated two-piece motor cover that is taller than later models, and came standard in 8/12, 10/12 (with the chopper and stator being reused from the BN44E Mobil Directo), and 9/12 dual tone. These early Allertors did not use chains for the rotator, instead using a rotating gear that rotates the siren around a very large stationary gear. These rotators are much larger than the chain driven rotators later Allertors used, and makes it very easy to spot. Gen-1 Allertors also use the smaller intake borrowed from the Mobil Directo. These were produced from 1968 until sometime in the very early 1970s. The very earliest of these had a vent on the side of the motor cover, which was later removed.
Generation 2: These are much rarer than the Gen-1. Gen-2 Allertors dropped the 8/12 and 10/12 option in favour of 9/12 dual tone. The rotor and stator were redesigned to be directional, which improved sound output greatly when the siren is wired in the right direction. The main difference between the Gen-1 and Gen-2 is that the motor cover is no longer enlongated, placing the projector directly on top of the rotator plate. It still uses a two-piece motor cover of the same height as the Gen-1, and ACA began experimenting with their chain driven rotators. A lip was also added on the upper projector. These were produced until 1972.
Generation 3: The third generation of Allertors came out in 1972. This is when the siren received the design it's most well known for. The intake was greatly enlarged in order to prevent snow and debris from getting into the projector and the motor cover was redesigned to be shorter and in one piece, and made entirely of fibreglass. This design decision forced ACA to add an indent into the projector to allow it to fit onto the rotator plate. Late in production, a few units were built using the 8-port rotor and stator from the Penetrator series, and had Penetrator projectors. These units were still marked as Allertor 125s, and had conical intakes. This design would be used all the way until the siren's discontinuation in 1980.
Something to note about Gen 1 Allertors is that the 9/12 and 10/12 rotors on them are bidirectional and very similar to Federal's SD-10, so reverse wiring doesn't affect them. However, the new 8/12 rotor was the first of ACA's sirens to use a directional rotor, so wiring it backwards harms sound output. The same applies to the 9/12 rotor on Gen 2 and 3 Allertors, which are also directional. In 1980, the Allertor was redesigned into the Penetrator-10 and 15, which replaced the giant projector with a simple horn and intake, which reduced costs and got rid of a lot of the Allertor's problems. The Allertor was sold alongside the P-10 for a short time before it was finally discontinued in favour of the P-10 and P-15.