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 moulded horn attached to an ABS base.It features 8 selectable tones with a internal adjustable volume controlfor both visual and audible alarm.2 models are availableHR-01D for supplies of 12VDC to 30VDCHR-01A For supplies of 24-28VAC