While nanotech advocates were touting the technology's surveillance and detection capabilities on Capitol Hill last week, an Ohio company was quietly experimenting with its own brand of surveillance.

CityWatcher.com, a private video surveillance company, has embedded silicon chips in two of its employees - the first known case in which US workers have been tagged electronically as a way of identifying them. The company said it was testing the technology as a way of controlling access to a room where it holds security video footage for government agencies and the police.

The two workers were implanted with RFID chips - inexpensive radio transmitters that give off a unique identifying signal - that until now have been implanted in pets or attached to goods so they can be tracked in transit. The chips are planted in the upper right arm of the recipient, and read by a device similar to a cardreader.

While the chips work with microtechnology rather than nanotechnology, the ethical concerns they raise will only increase as nanotech enables their size to decrease.

"There are very serious privacy and civil Liberty issues of having people permanently numbered," said Liz McIntyre, author of the book, Spychips.

"There's nothing pulsing or sending out a signal," countered Sean Darks, chief executive of CityWatcher, who has had a chip in his own arm. "It's not a GPS chip. My wife can't tell where I am."

Whether or not Mr. Darks wants his wife to know where he is may be a personal matter, but it's a small step from an RFID chip recognized by a card reader in a fixed location to a GPS-enabled one capable of revealing its user's location anywhere. Implantable GPS chips are already in use in pets and some infants (supposedly to prevent the theft of newborns from hospitals), so you can bet it won't be long before they start showing up in the workplace.