This ad dates to the early-mid 1980s. The siren advertised is the Penetrator-10 (P-10 for short) which is a 10-horsepower electric outdoor warning siren built by Alerting Communicators of America (ACA). ACA was the siren division of Biersach & Niedermeyer (BNCO), a company previously shown in the Mobil Directo ads. The P-10 boasted a rating of 125 decibels at 100 ft, with a double-sided 10 horsepower motor driving both the chopper (which makes the noise) and the chain-drive rotation mechanism underneath the siren using a gearbox. The siren used weather-resistant fibreglass for the projector and motor housing, which was something ACA was famous for as other companies used steel. It could also be single or dual-tone depending on what was needed.

The P-10 was released in 1980, replacing the Allertor 125 which was the same siren at its core, but used a similar projector to the Mobil Directo. This projector was found to suffer from water building up in the horn and freezing, which would jam up the chopper and burn out the motor. The P-10 didn't have this issue, which is why it replaced the Allertor. The P-10 was also sold alongside the 15HP Penetrator-15, and the monstrous 135 decibel Penetrator-50, which holds the record as the loudest electric siren ever built.

After ACA's bankruptcy and reformation into the American Signal Corporation in 1994, the P-10 was discontinued in favour of the P-15, which would be renamed to the RM-127 until it too was discontinued in 2002. The P-50 would be sold until 2007 under the name T-135AC. American Signal Corporation still exists today, selling the Tempest, E-Class, and i-Force lines of sirens.

This ad was released roughly around 1948, advertising the Mobil Directo air raid siren. I've posted an ad for this siren previously, which only featured the Mobil Directo's gas engine-driven BN52 model. This ad introduced a new variant of the Mobil-Directo, driven by a 10HP electric motor instead of the 25HP Wisconsin aircooled engine. This new electric model proved extremely successful, as engines require significantly more maintenance and are far less practical for siren use than a motor.

The new model, known as the Mobil Directo BN44E, saw widespread use across the United States and Canada. Rated at 126 dB @ 100ft for 10/12-port dual tone models to nearly 128 dB for 8-port single tone models, the BN44E was louder than most other sirens during the time of its production. The engine-driven BN52 would see sales dry up quickly after the BN44E's release, being discontinued in 1953. The BN44E would be sold until 1967, when BNCO was forced to stop making sirens due to stiff competition from Federal Sign & Signal.

BNCO would create a new division, known as Alerting Communicators of America (ACA) who would redesign the Mobil Directo into the Allertor 125, which saw the steel projector replaced with a fiberglass projector, and the dual belt-driven pulleys on the rotation drive replaced by a single chain-drive rotation mechanism under the siren. The Allertor 125 would be sold until 1981, when it was replaced by the Penetrator-10 which replaced the large projector with a simplified horn.

The Model M was an early electric siren first developed in 1920 by the Inter-State Machine Products Company, who would later rebrand to the Sterling Siren Fire Alarm Company based out of Rochester, NY. The Model M was perhaps the most popular and widespread fire siren sold in North America, with units being sold across the US and Canada in great numbers. It is said that nearly every volunteer fire department in the eastern US had a Sterling Model M, or Sterling's other sirens such as the Model 5VX or Little Giant.

Unlike earlier electric sirens such as the Denver sirens I talked about in a previous post, the Model M was designed from the ground up to be weatherproof. Reliability in an emergency is everything, and its designer, Merton C. Armstrong, knew this. The choppers are covered with rounded "sounders" which also direct sound downwards, the motor is protected by a cover, and the air intakes on each side had protective wire mesh to keep debris out. By 1928, the siren would be improved with metal louvres on the intakes to further protect it. The Model M used motors between 3-10 horsepower, could be single or dual headed, and were rated to roughly 115 decibels @ 100 ft.

The Model M as previously mentioned saw incredible success. As shown by a friend of mine who made a map of every known Sterling siren, these sirens found their way everywhere. Unfortunately, by the late 1970s, competition became too great as Sterling's 50 year old design became obsolete. Sterling went out of business in 1972, but its designs were bought by a new company known as Sentry Siren who produced the Model M until 1986.

Sentry Siren is still in business today, and many of its sirens are directly based on the Model M's chopper design which is a testament to how good the Model M was. Many Model Ms remain in service today, including several units which are roughly 100 years old. Van Alstyne, TX's Model M is speculated to be the oldest surviving Model M, and is currently still in service.

Video of an early single tone Model M in Van Alstyne, TX, presumably the oldest known Model M

Video of a later dual tone Model M with louvred intakes in Columbus Grove, OH

The Thunderbolt was one of the more unique designs for an outdoor warning siren. Instead of using a large chopper (the part that makes the noise in mechanical sirens) the Thunderbolt uses a small chopper through which pressurized air is fed from a Roots blower at the base of the siren. Because the feed of air is constant from the blower, the siren would not lose volume as it raised and lowered in pitch, unlike conventional sirens. Despite having a chopper diameter of only a few inches across, the Thunderbolt was more powerful than most sirens of its era at ~127 decibels @ 100 feet. The only siren that could beat it in 1952 was the Chrysler Air Raid Siren, which was powered by a Hemi V8 engine.

Thunderbolts were produced by Federal Enterprises (later Federal Sign & Signal and then Federal Signal Corporation) from 1952 to 1990. Federal's main competition, Alerting Communicators of America, famously created their own Roots-blown siren called the Hurricane 130 to compete with the Thunderbolt with questionable results. The design, while high-performing, was also maintenance intensive as the rotation mechanism and blower had belts that needed to be replaced on occasion. It would be succeeded by Federal's 2001 siren, which is sold today as the 2001-130.

Video of a Thunderbolt 1000

The "Denver Quadruplex" was a very early example of an electric siren, first invented and sold in 1914. The company who built these, the Denver CO-bssed William A. Box Iron Works Company , is generally credited for inventing the first practical electric outdoor warning siren, the Denver Type A, a few years earlier. Surprisingly, several of these remain in service today despite being 90-110 years old. These were originally meant for use in mines, but later found popular use as fire sirens. While manufacturered by William A. Box, the sirens were typically sold through vendors such as Hendrie & Bolthoff.

A friend of mine posted this to a Discord server I'm in and thought it was interesting. It's for the Peterbilt 451, a very unique and short-lived truck design that appears to have only been sold to a few companies and is now extinct. It appears to have combined a box truck with a semi truck.

This is a 1952 ad for the engine-driven BN52 model Mobil Directo air raid siren, which used a 25HP Wisconsin air-cooled engine to drive both the chopper (the noisemaker) and two belt-driven pulleys to spin the siren around. Later BN44E models would switch the engine to an electric motor. It was one of the first rotational sirens, and would later redeveloped into the "Allertor" and "Penetrator" electric sirens.