Now there's a app.
A Colombian company called Lemur Studio has designed a device that, if functional, could be worn over or in a shoe making it a metal detector. If it detected metal nearby it would send a signal to another device worn like a wristwatch which would allow the wearer to pinpoint the metal. The objective is to use it like a mine detector and save lives and limbs in mine infested areas. Presumably, false positives would not be so numerous as to discourage its use.
The company website says it's a design company, so someone else would probably have to actually make it. Their application for the World Design Impact Prize 2013-2014 can be viewed here. Glass-half-empty people will want to see the section following "Briefly describe the challenges the project currently faces":
At this time the problem that the project would be the technology in terms of the template because according to our research is carried out by means of nano-technology which would be very expensive to do in a country like Colombia and would require external entities, of other countries, for the successful completion of the project.
Hmm. There's the rub. An ordinary metal detector can be purchased for a few hundred dollars, and if that's out of reach for people living in land mined areas then high tech shoes might be a bit too pricy.
That aside, it is a neat concept, and maybe some outfit like Nike will just do it.