My experience has been that those door alarms are like car alarms. They go off so often, when folks hear them they are ignored so why stand there looking like an idiot? If someone ran after me for suspected theft, sure I'll stop and hand over my receipt and bag but I am not dumping my pockets nor taking the walk back to the managers office.
Forgetting the law for a moment, many large retailers have policies preventing employees from pursuing a suspect outside the store and only management, along with a loss prevention person can confront a suspect if at least two employees witnessed a person stuff an item in their clothing, never lost sight of the person and the suspect made an attempt to leave the store w/o paying for the item. Some will fake a shoplifting event to provoke a confrontation in hopes of a future lawsuit i.e. I stuff a CD down my pants in front of someone, turn a corner and dump the item in a bin or on another shelf.
My brother is a store manager for a large nationwide retailer and this is their policy... don't confront and don't chase. Keep eyes on and notify management and loss prevention. When he started with the company 25+ years ago, employees enjoyed chasing folks into the parking lot over a 200.00 drill.... until someone got shot or the incident when they tackled the suspect in the parking lot, broke out some of the persons teeth as a result and found no store merchandise on the person... no need to mentioned what happened after that ?$?$?$?$?$?
Regardless of the law, lawsuits have changed how stores react to suspected shoplifters.
"Detached reflection cannot be demanded in the presence of an uplifted knife." by Justice Oliver Wendell Holmes, Jr. in Brown v. United States, 256 U.S. 335, 343 (16 May 1921).