Sentry Defender

Sentry SS3 Defender
1st gen Sentry Defender
Company	Sentry Siren, Inc.
Produced	2001-2011
Type	Rotational Electromechanical
Sound output	127 dB @ 100 ft
Frequency	60 Hz
Horsepower	7.5 or 8 hp
Voltage	72 V DC 208-230/460 V AC 1 or 3 ph
Documentation	Product sheet

The SS3 Defender was a short lived rotational siren produced by Sentry Siren, Inc. as the company's first and only foray into producing rotational sirens. These sirens were plagued with issues and poor design, and as such are very rare to find in service today. As a result of its poor sales, as well as Sentry's overall preference for omnidirectional sirens, the Defender was discontinued and no further rotational sirens have been produced by Sentry.

History and Design

The SS3 was originally created around 2001, and was originally called the SS3. Sentry wanted to experiment with creating a rotational siren, and also at creating a DC-powered siren. The siren was created after requests from certain municipalities for a rotational Sentry siren. As part of a marketing effort, Sentry and its partner Sirens For Cities approached the original warningsirens.org forum with a contest for enthusiasts to pick a name for the siren. The name Defender was ultimately chosen, with the unknown winner of the contest winning one of Sentry's small sirens. The first units were produced in 2001 and sent to the city of Tuttle, OK. The very first Defender produced, serial number R001, was originally installed in Tuttle and was removed after Tuttle upgraded their system, and is now in private possession. These very early Defenders used an 8 hp 48 V DC motor, which was switched to 72 V DC on all later DC models.

First Generation

Sometimes called the "Roundback" Defender, the first generation Defender has a rather odd design for a rotational siren. The siren makes use of the Sentry 5V's rotor and stator, with either an 8 hp 72 V DC or 7.5 hp 230/460 V AC motor driving an 8-port single tone rotor, which allows the siren to reach 127 dB at 100 ft. A 16-port variant of the Defender was also available, although none are known to exist. The horn is similar in design to a Penetrator-10, with a large intake nose cone inside of a larger horn attached to the housing that surrounds the rotor. This horn is slightly longer on the top, almost forming a point. A large hollow housing contains the motor, which is suspended in midair, held up by the housing itself. "Sentry Siren" decals are located on the side of the housing, with "DEFENDER" labelled on the rear. First generation Defenders used a housing with a rounded top, similar to that of the Federal Signal 2001-SRN Roundback. Previously, it was presumed all Defenders had these housings until the second generation was discovered.

The first generation Defender has a complex, and somewhat unreliable rotation mechanism compared to other rotational sirens. On first generation units, a small DC motor drives a gear which is coupled to a gear reducer with another gear at a 90 degree angle, which is then attached to a planetary gear drive which turns the turntable that the rest of the siren is bolted to. The siren's brushes are located below the turntable. This design was notoriously faulty, as the gears between the motor and gear reducer were often not lubricated from the factory which led to shearing of the gear teeth, which causes violent shaking and stuttering to the siren's rotation. The rotator box itself is massive, and there is an enormous amount of empty space inside the rotator box, despite the mechanism itself being quite small. Because of the size of the rotator box, the Defender requires a special mounting bracket, which is twice as large as a standard Sentry mount. No first generation units are known to be in service today, though a few are in private possession.

Second Generation

Late in the siren's production, the siren would be updated with a newer, improved design that has been nicknamed the "Squareback" Defender. The rounded motor cover was replaced by a square housing with louvered ventilation holes to help cool the motor. The notoriously faulty and over-complex rotator was changed for the second generation Defenders, which instead directly bolted the motor to the planetary gear drive, which would then drive the turntable. This presumably improved the reliability of the rotator, though too few units exist to know for sure. Unfortunately, this was not enough to save the siren from being overshadowed by its competition and few units were sold. Three units remain in service today.

Issues and discontinuation

Unfortunately, the Defender was plagued with issues from the beginning. The first generation's rotator was notoriously faulty in design, with the gears often having their teeth sheared off from friction. This resulted in the siren violently shaking or stuttering as it rotates. While this would be corrected in the second generation, the siren still had other problems. The batteries these sirens used often ran flat, which caused the siren to run sluggishly or fail completely as it ran purely on DC without the use of an AC rectifier. This led to the siren becoming quite unreliable. AC powered Defenders did not have this problem, but these are rare. Defenders were also extremely vulnerable to corrosion, with its paint often flaking off and corrosion damaging the siren, which led to several Defenders being replaced. Due to its lack of popularity and its lackluster reliability compared to other DC sirens such as Federal Signal's 2001-130 and ASC's T-128, as well as Sentry's overall preference for omnidirectional sirens, Sentry ultimately opted to discontinue the Defender in 2011, after a 10 year production run. This would ultimately be the only rotational siren Sentry would make, as they decided that omnidirectional sirens were the superior option.

Today, Defenders are very rare to find in service due to the issues mentioned above and the low number of units produced, and most Defenders have been removed and replaced with more reliable sirens. Most known Defenders are the first generation roundback units, which was assumed to be the design for all Defenders until some second generation Defenders were found in the past few years. A few squareback Defenders remain in service to this day, notably in Coos Bay, OR, and Spring Valley Lake, CA. Some are original installs, while others were refurbished and reinstalled by companies such as Sirens For Cities. A few others are in private possession, including the first Defender produced.