A physical layer collision that occurs when a user presents a wallet or pass holder containing multiple contactless smart cards to an RFID or NFC reader. The reader's electromagnetic field powers up all the cards simultaneously, causing their microchips to transmit overlapping signals. This results in authentication failures, slow gate processing, or the wrong account being billed.
Tell the passengers to take their transit pass out of their wallet, we're getting card clash at the turnstiles all morning.
Transit authorities often run public awareness campaigns asking riders to isolate their travel cards to prevent clash.
Related terms
RFID
Radio-frequency identification, a system that uses electromagnetic fields to track tags.
Radio-frequency identification
A wireless tracking technology that uses electromagnetic fields to automatically identify and read tags attached to objects.
Near field
The electromagnetic region immediately surrounding an antenna where fields are not yet fully formed into a radiating wave.