How does the US know that I left?
Every time I leave Australia, I have to fill in an official form that the government collects to state that I've left the country.
However, when I left the US last week (after my first visit there), at no stage did anyone official verify that I was leaving the country. I checked in at the QANTAS desk at JFK and passed through TSA security there, and that's it. I got on a plane to LAX and then from LAX I didn't go through any checkpoints, and left the country. No immigration, no nothing.
Does the US government know that I've left the country?
They monitor your facebook wall, twitter, gmail.. you must have written something there about leaving the US..
@IKeelYou sure, but I could write anything I wanted there. I could write about how I plan on overstaying my visa after I've already left the country.
Yes, they almost certainly do know you've left. The US processes passport details for all air passengers through a system called APIS, and ties that to the electronic I-94 (arrival and departure record).
You can check your US arrival and departure history online. This allows you to verify their record of your departure.
Interesting. I'm guessing that if I check in, but never board the plane, then that information would also be passed through to the system, rather than having a standalone immigration system like I'm used to.
@MarkHenderson: If you don't board the plane, then you won't be on the airline's list of people who are on the plane.
When I re-entered the US after a cruise, the only question the officer had on seeing my passport was whether I was flying home (to Canada) or driving. Flying? OK have a nice day. I was told later it was because they know when you leave if you fly, and if I had said driving I would have been given a form to hand in when I left.
Does the US maintain arrival and departure info on citizens (as opposed to foreign nationals, which appears to be what the I-94 system is for)?
It is possible to leave the US without being "detected". For example, if you walk across Rainbow Bridge there is no opportunity to interact with CBP. The CBP know this, and you may get a bit of additional questioning next time you enter on the same passport, but it is not a big deal for an ESTA-eligible passport holder (in my experience).
@BobJarvis the I-94 information retrieval page allows one to enter a US passport. (The last time I used it I was checking my wife's I-94 records, and didn't think to see whether I could enter my US passport.) I do not have my passport with me, but I will try to remember to enter it and see what response I get. Come to think of it, I will also enter my European passport to see whether it has an entry there, too. When I flew from JFK to Gatwick a few weeks ago, I checked in with the EU passport, so maybe it has an entry in the database even though I never used it to enter the US.
With respect to "almost certainly know you've left" -- that's accurate. My wife's I-94 records showed a few instances where there was no record of her having left the country. That is, there were two consecutive entry records with no exit record in between.
@BobJarvis: No, they do not, or if they do, arrival and departure information for US citizens is not available through the online I-94 system.
@phoog Holders of two passports are of course an interesting test for the system described here. What would happen if you enter the US on one passport and present the other passport for the flight out?
@HagenvonEitzen Then your exit will not be logged. For many people this will not be a problem, but you may have to explain yourself to the CBP officer's satisfaction on your next entry. For certain categories of people on certain visas with certain histories you might be expected to provide more concrete proof that you left the country.