Here's a little gem from Roman Mars of the excellent podcast 99% Invisible. A recent episode was about sound design, specifically the NBC chimes, which are one of the few sounds ever successfully trademarked - worth a listen! Anyway, quoth Roman: "My current least-favorite sounds are from credit card chip readers that blare an obnoxious warning buzz that clearly signals to normal humans that something has gone wrong, even though it actually means everything went right, and it's time to remove your card." He's right: people do need to be reminded to remove their cards, but there's a huge disconnect between the intended message and the received message. Is there a more pleasant sound that also gets attention? Or can it be accomplished with any of the other senses? ("That smell means it's time to remove your card" - nah.) It's definitely a design problem in need of a good solution.