Sun Castle started to develop its digital door locks in 2005. SCG invested a substantial amount of money and resources to the design and manufacturing of SCG door locks. In 2008, SCG applied for a US patent of its electronic and mechanical design of the keypad lock, SK5. On June 9th, 2009, SCG received the certificate awarded by the United States Patent & Trademark Office. It not only acknowledges the outstanding work of the SCG R&D team, but also sets a great foundation of its product development.