It is a tiny radio device used by warehouses to keep track of stock and by conservationists to follow endangered species.
Now it can be used by schools for child protection and combating truancy, teachers at the Specialist Schools Trust technology conference were told.
But Bill Fowler, managing director of the education division of Cisco, the multinational networking company, said schools needed to grapple with the ethics of monitoring pupils with radio frequency identification (RFID) equipment.
Cheap radio tags, such as the ones used in London Underground's Oyster card, communicate with transmitters around a school, controlling access, monitoring pupils' movements, and even paying for canteen food.
Supporters say such monitoring helps keep pupils safe and makes truanting more difficult.
Mr Fowler said: "It's amazing the information that can be obtained from the tags. The question is: do we want it and how do we apply it?"
A trial of a system monitoring attendance at Brittan primary in California was dropped after complaints from parents and the American Civil Liberties Union.
In Japan, some schools use tags that trigger an email or text alert to parents, letting them know when their child arrives at classes or leaves for home.
Andy Chadbourne, marketing and communications manager for RFID suppliers Intellident, in Stockport, said the technology could be easily adapted for schools, although it would require trust between pupils and teachers.
"As with any system of this kind, you have to rely to some extent on the holder of the card to co-operate," he said. "There has to be trust on both sides. There is always the risk that someone holding the card could swap it with someone else. Pupils may forget the card as well, so there has to be a system in place to let someone into the school who does not have the card."
But that problem has been solved by US company, Applied Digital Solutions, which gained approval to insert a tag the size of a grain of rice under the skin.
Mr Chadbourne, whose company is installing the equipment in college and university libraries, said RFID would be better than swipe-card systems for controlling access to schools.
The scanners can read several tags at once without pupils taking the cards out of their pockets, preventing bottlenecks at entrances.
Pricing was "comparable" to swipe-cards and each tag cost about 25p, Mr Chadbourne said.