How the fire alarm system works

The intelligence of man and his exploitation of his mind was of great importance in the invention and development of tools and devices, and it also has a great role in providing means of protection and comfort for him. It reduced the risks of building fire, which reduced the material losses, and the number of human lives that were lost, whether due to fire, or because of smoke, and fumes resulting from combustion processes, so what is the principle of the work of the fire alarm? What are the systems on which it is based?