Unexpected sources such as bug zappers and radio towers can wreak havoc on a radio-frequency identification deployment. At least, that's what IBM Global Services has discovered at Wal-Mart Stores Inc.

IBM has tested RFID equipment in the back-room grocery sections of seven pilot Wal-Mart stores, in support of the retailer's RFID project, which officially kicks off Jan. 1. During the deployment, IBM consultants have encountered interference from handheld devices such as walkie-talkies, forklifts, and other devices typically found in distribution facilities. And nearby cell-phone towers, which transmit at the high end of the frequency band, sometimes leak unwanted radio waves into the RFID readers. Bug zappers in the back rooms of the test stores also caused interference.

"When you have a bug that hits the zapper, the RF power generated by the interaction with the bug produces noise in the coaxial cables," said Douglas Martin, an executive consultant at IBM Global Services, speaking at the Wireless Internet for the Mobile Enterprise conference earlier this month at the University of California at Los Angeles. Any company considering RFID implementation should conduct similar site visits to seek out possible radio-frequency interference, Martin said.

Wal-Mart has been working on solutions to the interference. "There will always be chances of interference with any RF system, RFID included, but by building intelligence into readers and devices you are then able to limit and react to the cause of the interference," says Simon Langford, Wal-Mart's manager of global RFID strategy. "For example, a reader detecting a cordless phone moving into the area could change frequency to filter out the interference."

Next, IBM is taking its experience abroad to China. Because many of Wal-Mart's suppliers manufacture and ship products from Asia, Martin said, a group from IBM is going to China in three to four weeks to work with companies tagging and shipping products directly from that region.