Developed by GTX Corp. and Aetrex Worldwide, the shoe is dubbed the Ambulator, and it "tracks the location and movement history of its wearer, relaying the information to a monitoring center through cellular networks," GTX chief executive Patrick Bertagna     wrote in an e-mail. Concerned family members and friends can log in to a Web site or receive alerts that will pinpoint the location of the person wearing the shoe, Bertagna added.

There are other GPS gadgets aimed at the Alzheimer's market. The major advantage of the shoe, said Carle, who's also a GTX adviser, "is that we're hiding the . . . technology." The idea is that a person with dementia might have bouts of paranoia but would be unlikely to remember there's a tracking device in his shoe and try to rip it out. Also, Carle said, because people with dementia often retain their habitual memory, they'll be likely to put on their shoes before going out.

The companies are planning to start selling the shoe next spring for $200 to $300, plus a monthly monitoring fee starting at about $18 per month. Some of the costs may be reimbursed by Medicare, Bertagna said.