In the episode of Stargate SG-1: "In the Line of Duty", Samantha Carter (Amanda Tapping) Gets possessed by a Goa'uld and gets discovered and captured by SG-1.

In the scene where Carter/Jolinar are in the brig, Teal'c (Christopher Judge) enters and exchanges words with Carter/Jolinar, Teal'c becomes agitated by what Carter/Jolinar said and hurriedly swipes his card and exits.

A swipe system only works if the stripe passes through the reader, after a brief validation process it would perform its duty, in this case unlock the door.

If you were paying attention, you would notice the magnetic stripe of the card is running under his thumb and not the extended portion of the card running through the swiper. The door shouldn't have opened.