Since I work both sides of this issue let me say this. If I can prove, with a doubt that you have stolen merchandise, ie. the standard, I saw you steal something, and never lost sight sight of you, or you have been video taped through the complete concealment, and denial of property routine, I will ask you to stop. If you refuse I will stop you. By whatever means are at my disposal.
If the buzzer goes off, and I don't have the evidence of proof, all I can do is ask you to step back inside to resolve the issue. If you politely refuse, you are free to leave. No law prohibits my asking this of you, but it does prohibit me from determining guilt based soley on the EAS.
Now if I ask you to step back inside, and you become unrully, loud, and obnoxious, then you have just changed things to creating a disturbance. If you get in my face, and threaten me, or attempt to intimidate me in a rude, or insolent manner you have just changed the game rules, and ball is my court.
Thus when the bell rings I politely decline to stop, and point out that the cashier needs further training, or the system needs adjusting. But then I don't steal.