While Samuel Tree, 68, was sentenced to three and a half years, his wife, Joan, 62, received 300 hours community work.
In August, the couple had denied fraud at the Old Bailey trial, claiming their device, sold as Alpha 6, did work.
Each device cost just a few pounds to make using a plastic box and antenna, but they were sold for as much as 1,171 pounds (USD 2,000).
Tree claimed the detectors could track down missing people if a photograph of them was placed inside - a technique he said he had used to search for Madeleine McCann, who went missing as a toddler in 2007, and two other children.
Police said one of the fake gadgets, assembled out of plastic imported from China, was bought for 500,000 pounds.
The bogus contraptions were based on a novelty "golf ball detector" called the Gopher which sold for around USD 20 (12 pounds) in the US.
Businessmen James McCormick and Gary Bolton were jailed last year for versions of the scam, which saw the devices used at check points in Iraq.
Bolton claimed his GT200 device could detect anything from cash and land mines to ivory and tobacco.
He worked closely with the Trees after meeting them at an arms fair, police said.
Detective Constable Joanne Law, from City of London Police, said the couple were "driven by personal greed".
Despite the convictions, versions of the fraudsters' devices are still being used by the Egyptian military to detect HIV and hepatitis, on Iraqi checkpoints, and to protect shopping centres in Pakistan, the BBC reported.
