Over/Under The Counter

I was in a local drugstore and noticed this large plexiglass case enclosing many of the painkillers and other items.  These were over-the-counter medications, but if you lifted the cover, an alarm would go off--and stop once you closed it.

So you could reach in, take something and buy it no problem.  Why the alarm? Drugs behind the counter are heavily protected, and with good reason, but these were available to anyone.  Who were they trying to scare?  "Hey, we know you've got something perfectly legal, but don't forget we've got our eyes on you!"