When a proctor checking people in sees somebody with one of those watches (especially if the person is wearing it on their wrist, since they are super fashionable! lol), the student is pulled aside, similar to getting sent to secondary screening at an airport, and given a little talk and an option.
What the proctor would say would go something like this:
Joe/Jane Blow student, are you sure you are really prepared to do your best and should take the LSAT today? It will use up one of your three chances and be noted on your permanent record with a number or one of those other marks depending on what you do. This is your last minute chicken-exit opportunity. Right now you can decide not to check-in and just go home. If you choose this option your registration will be withdrawn and nothing will show up on your record. Otherwise you can decide to head on in and hopefully you are prepared to and will do your best. Option #1 or #2? You have 10 seconds to decide.