The Ex Signalling Hooter HD22 is
designed for calling, warning, and signalling in Zone 22 explosive environments. The hooter is available in the usual
supply voltages and produces a sound volume of approximately 108dB(A) at a distance of 1 meter. The driver is made up of
a strong unpolarized electromagnet controlled by alternating current and strikes a membrane at 100 - 120 times per second.
The DC version uses an electronic contact breaker.