Simplex 4904-9139 Category : Simplex I believe that this strobe plate was designed to be used with bells, such as the Simplex 2901-9333. Brand SimplexModel 4904-9139Manufacturer SimplexType Alarm (Strobe Plate)
System Sensor SP1W2475ADA Category : System SensorThe strobe portion can detach from the speaker body.
Simplex 2901-9517 Category : SimplexThis is essentially the AC-powered version of the Simplex 2901-9833.
