This LED strobe sounder combination is an ideal product for HVAC related warning.
It can be used inside or outside.
Made out of flame retardant ABS and red polycarbonate lens.
It has a two part molded horn attached to an ABS base.

It features 8 selectable tones with a internal adjustable volume control
for both visual and audible alarm.

2 models are available

HR-01D  for supplies of 12VDC to 30VDC
HR-01A  For supplies of 24-28VAC 

24VAC Diagram

PDF document here  https://ln5.sync.com/dl/7b64088b0/twriyf7y-7asvh8uw-6uy9dwgb-xb38q36a