The Tempest series is not just one variation of one siren; it is a chain of many sirens ranging all the way from the Penetrator-50 (1980's) to the Tempest T-135, which was released in 2007.
There is many different types of Tempest:
T-112/T-121
T-128/T-135
The Tempest 112 and 121 are similar to Federal's Eclipse 8 and NH, they are horned omnidirectional stand-still sirens. The 112 is a no-horn version of the 121 and is meant for small towns who need cheaper sirens. The T-128 is a siren that has a decibel count of 128. The T-112 has 112db at 100ft, T-121 121db, and so on. The T-128 is similar to Federal's 500. The T-135 is a rework of the P-50, but the T-135 is in a T-128 shell. The T-135 is ASC's newest mechanical siren, being released in 2007.
Official ASC photo of all mentioned sirens (excluding P50)