Smoke detector adapted to a smoke sensing apparatus

A smoke detector is disclosed which comprises an inner electrode, an intermediate electrode with a hole for passing radioactive rays therethrough, an outer electrode having openings for allowing smoke to flow therethrough, and one radioactive source, the inner and intermediate electrodes forming an inner ionization chamber, the intermediate and outer electrodes forming an outer ionization chamber, the radioactive source being disposed in the inner ionization chamber. A proper quantity of radioactive rays from the radioactive source is applied into the outer ionization chamber through the hole provided in the intermediate electrode