Since they are always ready for use, mechanically powered flashlights are often kept as emergency lights in case of power outages or other emergencies. They are also kept at vacation homes, cabins, and other remote locations because they are not limited by battery shelf life like ordinary flashlights. They are considered a green technology, because the disposable batteries used by ordinary flashlights are wasteful in terms of resources used for the amount of energy produced, and also contain heavy metals and toxic chemicals which end up in the environment.