Radio frequency identification, or R.F.I.D., refers to a variety of wireless technologies that create communication between a tag and a reader. R.F.I.D. can be used for long-range communication through ultra-high frequency, or U.H.F., tags or for very close communication using near field communication, or N.F.C., tags. These tags can be embedded in wristbands, badges, plastic cards, and other products that guests carry at an event. Here are examples from six recent events that have used wireless technology.