I got a terse e-mail from CMU this morning telling me that my card was found in the ATM over at the University Center. I've never left my ATM card in any other machine, anywhere, but it's happened twice at the Citizen's Bank ATM here at CMU. I decided to figure out why.

There are actually two Citizen's Bank ATMs side-by-side in the University Center. One has a swipe card reader. The other holds the card until the end of the transaction. I worked at a bank when I was in college, and our ATM was forever eating people's cards, so I'm biased toward the first type of machine. I swipe my card, then put it back in my billfold before I even enter my PIN. If I choose not to print a receipt, I can just pick up my money and leave. Pretty convenient.

Today though, that machine was broken--forcing me to use the other one. Objectively, it works just fine. It even beeps annoyingly until you remove your card. So what's the problem? The PNC Bank ATM around the corner acts the same way, but that machine is consistent in its behavior, so I've never had a problem with it. The Citizen's Bank ATM would probably be okay if it was standing by itself, but for some reason they've installed two machines with radically different card handling schemes right next to each other. It's easy to mix them up.

When I went to pick up my card at the information desk, they pulled out a binder for me to sign. As I looked for my name, I saw dozens of entries with the label "BANK CARD." Citizen's Bank probably doesn't even know there's a problem.

I found your site while looking for an article on this topic and couldn't resist commenting. I spent several years researching these "postcompletion errors" (Byrne & Bovair, 1997), which the second machine invites because of the way it's designed. Essentially it requires you to execute some step (get card) post completion of your primary goal (get cash). The beep is one way to address the problem, but obviously it's not robust enough a solution (thus the sliding card atms and ones where you take your card back immediately after inserting it, cropping up).

Just from skimming, it seems you went to CMU and do technology design? HCII maybe? Perhaps you even know of Byrne (my former advisor), who used to work with John Anderson in the psyc dept. What a small world that'd be.

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