A fire alarm call point (also referred to as a red manual call point or a break-glass call point) is essentially a small box, mounted on a wall which contains a button or a lever that allows you to manually trigger the fire alarm in a building.
A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about 150 mm(6 in) in diameter and 25 mm (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system.