Abstract: A housing assembly of interlocking parts for a dual-chamber ionization smoke detector in which the assembly has a single universal smoke detector head that can be readily twist-locked in one of a plurality of selectable adapter bases appropriate for a particular power source. The smoke detector head includes an interlocking assembly of an ionization chamber module protectively housed between an adapter base cover and a smoke detector cover. The detector head may be removed as a single subassembly from a particular adapter base, and additionally the detector head may be readily disassembled to remove the ionization chamber module for repair or replacement. The smoke detector cover has a dish-like configuration formed with an integral frusto-conical section. The interior of this section is formed with smoke deflector ribs. The cover protectively covers both the ionization smoke chamber and the adapter base.