To checkin online, with Costco, I book on Costco Travel site (not sure why one would avoid this and enter the codes manually on the Alamo site? it is very convienent to have all pending reservations in one place for me.) Then I get a confirmation with a Costco reservation number and an Alamo reservation number. I go onto the alamo site, using their confirmation number. I am also part of their Insider club. Using that Alamo confirmation#, I can check in online, and even ADD the free second driver, if necessary. Then this lets me print out a paper with a barcode checkin thing. Pick the car and quick exit.