Rivers, inland lakes and artificial lakes in temperate climates are fragile and prone to accidents when the water bodies freeze into ice. Ice Manhole Cover works as a warning for unsafe ice and minimises the frequency of unfortunate accidents on ice.
With the Ice Manhole Cover placed on the ice, when the ice is about to melt, or when it is not strong enough to withstand human weight, the top of the cover will emit a red light as a warning. When ice is strong enough to hold people, the top of the cover shines green as a "safe" signal. In other seasons, the underside of this device can be used to measure water quality and temperature.