The DSC MX926 is an addressable smoke detector. These are for use with a Qolsys IQ Pro panel. Once you add a HSM3105 MX addressable loop module to the IQ Pro, you can then use the various MX devices of your choice. The MX926 uses the optical method to detect smoke. This is best used in places where the potential fire is slow-burning. The MX926 also has a small footprint, coming in at only 4.252" inches in diameter.