Emergency evacuation sirens have become common all over the world, and can warn the inhabitants of a building or community of fire, extreme weather or enemy attack. People have always found it important to warn others of impending disasters, and the first audible fire alarm or siren was the playing of drums or wind instruments. In fact, some primitive tribes still use this method to warn others. Church bells were widely used during the Middle Ages all over Europe to alert people; often the bells in different churches would form a chain, one church alerting the next to ensure everyone heard them. With more wars in the 20th century, evacuation sirens became more commonplace, as well as more powerful and effective, when powered by electricity. Today’s emergency sirens are sophisticated and effective, and as technology evolves, are typically controlled by a computer rather than a person.