2005, when five companies, including Danfoss, Ingersoll-Rand and Leviton Manufacturing, adopted Z-Wave. They formed the Z-Wave Alliance, whose objective is to promote the use of Z-Wave technology, with all certified products by companies in the Alliance interoperable. In 2005, Bessemer Venture Partners led a $16 million third seed round for Zensys. In May 2006, Intel Capital announced that it was investing in Zensys, a few days after Intel joined the Z-Wave Alliance. In 2008, Zensys received investments from Panasonic, Cisco Systems, Palamon Capital Partners and Sunstone Capital. Z-Wave was acquired by Sigma Designs in December 2008. Following the acquisition, Z-Wave's U.S. headquarters in Fremont, California were merged with Sigma's headquarters in Milpitas, California. As part of the changes, the trademark interests in Z-Wave were retained in the United States by Sigma Designs and acquired by a subsidiary of Aeotec Group in Europe. On January 23, 2018, Sigma announced it planned to sell the Z-Wave technology and business assets to Silicon Labs for $240 million, and the sale was completed on April 18, 2018. In 2005, there were six products on the market that used Z-Wave technology. By 2012, as smart home technology was becoming increasingly popular, there were approximately 600 products using Z-Wave technology available in the U.S. As of June 2022, there are over 4,000 Z-Wave certified interoperable products. Interoperability Z-Wave's interoperability at the application layer ensures that devices can share information and allows all Z-Wave hardware and software to work together. Its wireless mesh networking technology enables any node to talk to adjacent nodes directly or indirectly, controlling any additional nodes. Nodes that are within range communicate directly with one another. If they aren't within range, they can link with another node that is within range of both to access and exchange information. In September 2016, certain parts of the Z-Wave technology were made publicly available, when then-owner Sigma Designs released a public version of Z-Wave's interoperability layer, with the software added to Z-Wave's open-source library. The Z-Wave MAC/PHY is globally standardized by the International Telecommunication Union as ITU 9959 radio. The open-source availability allows software developers to integrate Z-Wave into devices with fewer restrictions. Z-Wave's S2 security, Z/IP for transporting Z-Wave signals over IP networks, and Z-Wave middleware are all open source as of 2016. In 2020, the Z-Wave Alliance ratified the Z-Wave specification, adding the application to open-source development. The Alliance Technical Working Group manages Z-Wave