I went through security at the C/D gates this morning (by the way, the BKSX machine to the far right is down for maintenance, woo hoo!). I am flying AA today to JFK and wasn't sure if the PreCheck thing would work since American only has three gates at SEA, but sure enough my boarding pass triggered the guy to pull his chart out and add a tick mark to it. I'm happy about this even though it means I'll have to go through security at the D/N gate checkpoint for an AA flight, which means a long walk back the other way - but it's still worth it to avoid the rest of the carnival!