Airports are made and operated for safety. Today, people must walk through a metal detector, a machine that can tell if metal goes through it. If it makes a noise, the officers will make that person take off all things on them that are metal. They also have X-ray machines that can look into luggage. If officers find items such as weapons, or anything that can be used to kill people, that item (and the person who has it) are taken away and possibly arrested. As well as this, passengers are not allowed to bring bottles or containers with over 100 ml of liquid onto the plane because they could be turned into bombs. Therefore, all water bottles must be emptied before entering the secured area.