I was in a department store last week, and noticed the same chirping coming out of the Men's department. This seemed odd, so I tried tracking the noise down (a tricky endeavor, since the sound echoed, and seemed to move around the store). Eventually, I was standing next to a rack of leather jackets when one of them chirped. The culprit was an anti-theft tag. I asked an employee, and they confired that the tags did that when they ran low on charge, but that "we get use to the noise, and hardly notice them anymore."
There are probably several lessons here about designing systems that need to raise periodic alarms.