The Ca-425 is just a BRAIN, And Its sold Separately... The Brain is 40 bucks on EBAY!... So Basically its a Deal! Cause the CA-645 is 129.99 on EBAY alone...! The CA-425 doesnt come with Remotes and Siren, and Remote start unit, and the Shock Sensors, ITS JUST A BRAIN!!!.. So this CA-645 is an Upgrade for the BRAIN!