[jokecamp]

Makes me think of the not-so-fun idea that stadiums would need to prevent "seat pirates." Ushers get an app that indicates if there is a butt in a seat for a ticket that was never used. They just need a sensor on the seat to indicate the status.

Much easier to enforce when you don't have to ask people to see their tickets. Everyone hates that.

[relic]

This made me think that thought as well. Judging by the number of ushers usually at events like this, in practice they probably wouldn't even need sensors on the seats. The ushers probably know the system better than anyone, and given a list of seats that should be empty, I'd bet that it would not take them very long at all to check if someone was sitting there.

[abelcuskelly]

RFID tags on tickets could accomplish this and have been being tested for a while now but haven't got much adoption yet unfortunately. Hopefully more soon. http://www.theregister.co.uk/2005/04/04/world_cup_rfid/

[wcfields]

You have ushers at certain gates with scanners, only people with tickets that are allowed in that section. You can allow multiple gates nearby, but most stadiums are setup that there's really only one/two entrances to your section. You can't really seat-pirate beyond at most a few dozen rows.