A couple face a jail sentence after being found guilty of making fake bomb detectors in their back garden which they claimed could find missing Madeleine McCann.
Husband and wife Samuel and Joan Tree made "outlandish claims" that the dud devices could be used to track down explosives and drugs.
But the detectors, known as Alpha 6 and marketed through their company Keygrove, were nothing more than plastic boxes with an antenna strapped on to them containing ripped up pieces of paper.
They were sold for as much as $2,000 (£1,171), despite costing just pounds to produce.
Judge Richard Marks QC gave the pair bail ahead of sentencing but warned them: "You must understand that all options are open to the court and the strong likelihood given the offence of which you have been found guilty is a custodial sentence."
The Trees are understood to have made in hundreds of thousands of pounds after making up to 1,500 of the devices in the back garden shed of their semi-detached home in Dunstable in Bedfordshire.
Mr Tree had claimed it was possible to find people by putting a photo in the box.
He said he had used the method to look for Madeleine and two other children who vanished in Norfolk some years ago.
One of the boxes was found to have a photograph of missing Madeleine inside, which had been cut into pieces.
Prosecutor Sarah Whitehouse QC told the Old Bailey: "They claimed that this Alpha 6 was capable of detecting the presence of drugs and explosives and other substances and objects.
"They even claimed on one occasion that it is capable of finding particular people, most notably Madeleine McCann.
"Despite the fact that these plastic boxes plainly could not work, people did, astonishingly, buy them."
They claimed the Alpha 6 could detect substances as small as 15 billionths of a gram at a range of up to 500 metres and was powered by nothing more than static electricity from the user's body.
The prosecutor said: "The impression given is one of sophistication and effectiveness based upon scientific principles.
"The reality was that Samuel and Joan Tree were assembling the devices in the garden of their semi-detached house in Dunstable with plastic boxes made in China and glue and bits of paper."
They were both found guilty at the Old Bailey on Friday of making an article for use in a fraud between January 2007 and July 2012.
Detective Constable Joanne Law, who led the investigation for the City of London Police's Overseas Ant-Corruption Unit, said: "Sam and Joan Tree are criminals who put lives at risk when they chose to cash in on detectors manufactured to supposedly locate anything from hidden explosives to missing persons."
The couple, of Houghton Road in Dunstable, Bedfordshire, will be sentenced on a date to be decided next month.
Additional reporting by Press AssociationReuse content