John Williams, who directs the Auto-ID Labs at MIT, a leading center of RFID research that is not connected to SNIF, says that the technical details are unclear but that "they seem to be using the 'handshake' idea that the cell-phone companies are using, so that cell phones know when other cell phones are nearby." But SNIF declined requests for interviews, and a representative said in an e-mail that it's instituting a "media blackout" until Federal Communications Commission testing of its product begins next month.

Whatever the details of the company's wireless methods, the larger question is whether dog owners will rush to adopt the concept. Valdis Krebs, the developer of software for social-network analysis, doubts that people will want to fork over money for a device that essentially only digitizes what they're already doing: meeting people while on walks with their dogs. "I don't need a device to tell me whether my dog is happy with other dogs," says Krebs, who happens to be a dog owner. "And just because I meet another dog owner doesn't necessarily mean we'll share the same tastes in movies or restaurants."

But Rheingold says that he's been amazed at what he calls the "passion-centric" nature of the pet market. Through Dogster, he's seen people form long-lasting friendships, all because they met online through their dogs. More than 280,000 dogs are currently listed on the Dogster site.

SNIF's website says that its tags are going on sale in boutique stores in Boston in November, and it gives an online form for preordering the tags. There's no word yet on what the service will cost.