That's the ionisation type. There are others, such as optical (beam of light broken by smoke) and heat detectors which use a thermocouple detecting either a fixed temperature or a sufficiently rapid rate of rise. There is another, aspirating, but that is not used in homes, it relies on sampling air and creating a rapid pressure drop at intervals. If there are hygroscopic nuclei in the air (smoke or the precursors) a "cloud" will form and that is optically sensed, they are used in warehouses typically, because they are good for early warning of fire, before it even starts often (strike a match and it goes off even if you blow out the match immediately).