A fire drill is a sudden practice event, where people leave a building. They are practicing what they would do if there was a fire in the building. The event is started when the fire alarm goes off. The fire alarm sound can either be a continuous metal bell, a horn or a two-tone siren. Some old alarms in the UK like the Chloride Gent Warbler will curve between the two tones. The entire building is evacuated and everybody leaves the building using the nearest fire exit. At a school, college or university, the teacher or the lecturer counts the people outside to find out if anyone is missing. Sometimes people are evacuated when a drill is not scheduled by the school. This is called a false alarm. There are rules and regulations in place where fire alarm devices should be tested on a weekly basis. If the fire alarm sounds and the building is not evacuated, this may be due to the a scheduled fire alarm test that people already know about.