When you enter a security line, tweet this message:
#airportsecurity xxx in
and when you leave the line, tweet:
#airportsecurity xxx out
is an airport code like "ord" or "lax". The airport code is optional for the second message. Also, "in" and "out" can come before or after the airport code.
The following example will work too:
I'm going to #airportsecurity in ord and I hope I make my flight.