McAfee, the man originally behind the famous McAfee antivirus software, told about 300 engineers, musicians and artists at the San Jose McEnery Convention Center that the device, called "Decentral," would cost less than $100 and block all attempts at government surveillance.
"There will be no way (for the government) to tell who you are or where you are," he told moderator Dan Holden at the C2SV Technology Conference + Music Festival.
He added if the US government bans its sale, "I'll sell it in England Japan, the Third World. This is coming and cannot be stopped."
McAffee said the gadget is called Decentral because by communicating with smartphones, tablets and other devices, it will create decentralised, floating and moving local networks that can't be penetrated by government spy agencies, and the first prototype would be finished within six months.
The 68-year-old British-American entrepeneur made headlines last year when he was arrested for illegally entering Guatemala, where he was seeking asylum. He then reportedly suffered two heart attacks while in detention, but later claimed he had faked them.
As first reported by Mercury News, McAffee confirmed to conference attendees the device's design is ready to go, and its range will be three blocks in the city and a quarter mile.
It would be compatible with both iPhones and Androids.
He said he had the idea for the device for a long time before Edward Snowden leaked revelations around the NSA's widespread surveillance of US citizens, but after it happened "it became the right time" to make it real, he said.