If you did some skiing last season, you might have used a lift ticket with a tiny RFID tag buried inside that activated the chair lift gates -- and tallied how many runs you took.

Look closely, and you’ll see tags that use radio frequency identification everywhere, from lift tickets to credit cards and passports to pets. Companies like Wal-Mart have used RFID for years to track pallets of merchandise from the warehouse to the store shelf. But as the technology shrinks and costs drop, RFID is showing up in all kinds of consumer settings, including applications such as dressing room mirrors and smartphones.

RFID tags are even being used to track people, a development that has security experts and privacy advocates more than a little concerned. “There are some ethical and moral responsibilities there,” says Curtis Baillie, a longtime retail security consultant in West Chester, Penn. “There is great potential for it to be misused if somebody wanted to.”

RFID uses a thumbnail-sized tag with an antenna and tiny chip that stores information. A separate reader sends radio waves to the antenna, transmitting information from the chip. Some RFID readers only pick up data if a tag is less than an inch away. Others can scan data in a tag from across the room or farther.

RFID is everywhere
You can find RFID technology in:

• Charge cards Issuers, including Citibank and American Express, are putting RFID chips inside charge cards, and processors are placing RFID readers in existing charge card payment machines. Instead of swiping a card to pay for something, you just tap it on the machine.

• Cell phones You might need to carry little more than your phone when you run errands in the near future. In a trial that started earlier this year in Spokane, Wash., customers of a local bank can use Nokia cell phones loaded with a virtual credit card and RFID chip to pay for movies, lunch at McDonald’s or merchandise at 7-Eleven by tapping their cell phone on specially equipped readers.

• Retail applications A British company, Paxar, is testing an RFID reader that doubles as a dressing room mirror. Soon, you might try on an item and data from its RFID tag -- size, color, availability, recommended accessories -- will appear in the mirror.

• Patient care Doctors have started using sponges with RFID chips in them so the sponges aren’t accidentally left inside patients after surgery, according to industry reports.

• Pets and livestock Conscientious pet owners have put RFID chips in puppies and kittens for years. According to RFID Journal, an industry publication, the U.S. Department of Agriculture is close to adopting a national plan to put RFID tags on cattle, pigs and other livestock to make it easier to trace animals in the event of an outbreak of mad cow or other diseases.

RFID on the ski slopes
Mt. Bachelor ski resort outside Bend, Ore., started using lift tickets with RFID tags during the 2006-2007 season. The lift tickets help skiers get through chair lift gates in one second instead of the three seconds or longer it used to take, which quickly adds up on a busy ski day, says John McLeod, the resort’s finance director. At home, skiers can enter an access code from the ticket on the mountain’s Web site to see how many runs and total vertical feet they skied in a day or season. The resort uses this data to track what runs and lifts are used most frequently. This data is then given to information managers, who use it to decide when to open chair lifts and how to price lift tickets. “I’m very pleased with how it’s going,” says McLeod.

Using RFID tags to aggregate consumer information sounds harmless enough. But as the technology becomes more ubiquitous, it raises concerns about privacy. The issue was highlighted after the United States began putting RFID chips in passports in 2006. Organizations like the Center for Democracy and Technology, a Washington, D.C., consumer rights advocate, suggest that companies always tell people when RFID tags are being used, take steps not to collect or share information inappropriately and make sure data that is collected is protected from unauthorized reading or “skimming.”

Some states have taken matters into their own hands. In March, Washington state passed a so-called anti-skimming law making it a felony to surreptitiously scan RFID tags. In 2007, at least 13 states introduced some type of legislation about the use of RFID, according to the National Conference of State Legislatures.