He was hired as a technical consultant for the Norwegian High Command after the war. In 1947 he started the company Simonsen Radio in Oslo, and in 1957 the company Simonsen & Mustad followed in Horten. He received initial capital from Halfdan and John Mustad. The brand name Simrad became known in the communications business, and was leading in echo sounding equipment. He backed out of these companies in 1968 and started Simonsen Elektro (in Oslo) in 1970 and Simonsen Elektro Løkken (in Løkken Verk). These companies produced automatic cell phones, in the NMT 450 system, and were leading in the Norwegian market until the 1980s.
