Give out an audible alarm alters dysfunction of the APU system of a shipping aircraft.
It also allows the crew to warn the ground staff during parking maneuvers.
It gives out a 600 – 700 Hertz frequency.

This sound warning is conceived for operating in extreme temperatures, from -55° C to + 70° C.
Sound level:  >100 DB at 3 Feet at 28VDC.
Intensity: 0.5 AMP under 28VDC.
Operational tension:  20 to 28 VDC.