Snow guards are rooftop systems that allow snow and ice to fall off in controlled amounts or allow snow and ice to evaporate completely. Using snow guards prevents the sudden fall of snow and ice from a roof, known as a "roof avalanche". A roof avalanche can cause harm to people, pets, cars, landscaping, gutters, plumbing vents, lower roof areas, skylights and anything else that might be in the immediate distance below your roof. Snow guards have been used for hundreds of years and have historically been used on slate, tile and metal roofs. The first snow guards were tree limbs that were connected to the eaves on a roof, with rocks placed atop the limbs, to hold the snow back.