The 2001 series is a warning siren intended as a successor to the Thunderbolt series. The 2001 is a common sight in the United States.
The 2001 was first introduced as the 2001-DC Roundback, produced from 1988-1990. It used the same rotator assembly as the Thunderbolt. It earned the "Roundback" nickname due to its distinctive chopper housing, which is rounded at the top.
Next comes the 2001-DC made from 1990-1995. These models used the same rotators as the Thunderbolt, but with a different motor. The main difference is that the chopper housing is square-shaped.
The 2001-SRN, produced from 1998-2003, is one of the more common models in service today. It has a small Federal Signal on the center cone and a larger horn. The rotator assembly is shared with the Thunderbolt, this being the last model to use that rotator.
Next comes the 2001-SRNB, made through 2003-2006. This was the first of the 2001 series to use a rotator not shared with the Thunderbolt. It used a gear-driven system, unlike the older belt-driven units. Otherwise, it is largely identical to the 2001-SRN.
Today, the 2001-130 is the only model of 2001 available new today. Production began in 2006. The 2001-130 was the first model capable of producing 130 dB at 100 feet. It achieved this in part due to a larger motor. To fit the new motor, the motor housing was made taller.
In 2014 the 2001 Equinox was introduced. This model is identical to the 2001-130, but it uses an 8-port chopper instead of a 12-port chopper. Due to the new chopper, its pitch is lower, with a sound akin to that of a Federal Signal 508 or an ASC T-128.