Designed for use in unattended battery installations or remote shelters containing gassing lead acid batteries and charging systems, HGD-3000 protects against hydrogen gas buildup while also detecting smoke, temperature, loss of power, and intrusion. Unit mounts to wall, ceiling, or optional junction box and turns on exhaust fan when hydrogen gas levels reach 1%; alarm – local 80 db horn, flashing red LED, and dry contact switch closure – activates at 2%.