That happened to me with a bag I did a charge send on. I took it to my local FP store and they deactivated it. It was sewn into the bag, it was a baby bag. This was several years ago, though. They may not sew them in anymore.
Pretty much every coach bag I have bought has set off a sensor at some point. The good news is the tags are removable and your bag wont set off a sensor once you remove the tag. I've been to stores that know it's a Coach bag because it set off the alarm. Lol. It is a way to announce what you're carrying. Whether you want to announce it or not.
Glad you found the culprit! This kept happening to me a couple of years ago and I had no idea what was causing it. When I was leaving Lane Bryant and it happened the associate told me it was a common issue with Coach. I proceeded to go to the mall bathroom and dump all of my crap out on the counter and FINALLY found it.
Haha I had no idea how common this was! This has happened to me also. Coach loves to shove those security bars deep into some pocket. Now I check every nook and cranny of my bags
They aren't sewn in, it's loose piece. All the bags shipped from the warehouse have a sensor in them, even the ones sent out to customers from the FOS sale. When bags are transferred from the full price store to the outlet, they have to add the sensor when they unpack them. When you make the purchase, they run them over a deactivator, but if the sensor isn't removed from the bag, it can become reactivated later, that's why all of a sudden you might set off alarms.