I'm going to blast a loud alarm noise to get the cashier's attention
I hope you aren't really serious, what are you going to accomplish with this alarm?
I want her to see me, can she stop swiping and just obey my orders?
I do not think that you should do that. The cashier is just trying to do her job, it is rude to try to startle her just for a giggle.
I have got nothing to lose.
But don't you want to be respectful of the other people there? There are other ways to get the cashier's attention without making a rude and disruptive scene. You might embarrass her and ruin her day, or her boss might blame her for this.