As customers enter Tower Records, most pass by the inconspicuous maroon door on the right-hand wall without thinking twice. If they do notice it, chances are they guess it is a break room, a storeroom or an employee restroom.

But in this little room, a man in a bright yellow Harvard sweatshirt sits and watches the closed-circuit monitor in front of him, which shows a teenage girl carefully peeling the security tags off two compact discs and slipping them into her friend's backpack.

The girls stroll around the store for a while, trying to evade suspicion with their artificial nonchalance, but to no avail. Just as they think they're home free, the man in the yellow sweatshirt saunters down the ramp to the front door and politely requests that they follow him back inside.

Busted.

The man in the yellow sweatshirt is Olyver W. Haynes, Tower Records' loss prevention agent. His job is to monitor the store's state-of-the-art security system.

Using controls that look remarkably like video game controls, Haynes can rotate each of the system's several cameras 360 degrees, so no area of the store is left unwatched.

The system also allows Haynes to zoom in. Saved in the system's memory is footage of the girl's fingers peeling off the security tags-from two different angles.

Security systems like this one have helped to bring the incidence of reported shoplifting in Harvard Square down 21 percent in the past year, a year in which the incidence of shoplifting in Cambridge as a whole only decreased one half of one percent.

But the decrease in the number of incidents recorded in the police blotter does not necessarily translate to a corresponding decrease in the total amount of theft.

Square proprietors and police agree that the decrease is not as encouraging as it may seem, because factors such as a decreasein the percentage of incidents reported or adecrease in the percentage of shoplifters who areapprehended are more likely to blame.

"It's very driven by the stores, by whetherthey have security systems," says a CambridgePolice officer, who asked not to be named.

So, rather than boding well for the city'sstores, the decrease means they are letting theshoplifters slip by.

"My feeling is that shoplifting is up," saysEve M. Turner, regional loss prevention managerfor CVS drugstores.

"And we have definitely seen an increase inprofessional shoplifting, as opposed to a studentcoming in and picking up a pen on his way toclass," she adds. "That's surprising because theeconomy is strong right now."

Even with its 21 percent decrease, HarvardSquare still claims two places on the policedepartment's most recent list of shoplifting "hotspots." The list, which is updated quarterly,includes 16 of the city's 870 census blocks.

People like Olyver Haynes and stores like TowerRecords are doing all they can to ensure that thedecrease in shoplifting recorded in the policelogs will translate to an actual decrease in theirstores.