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They are not metal detectors. They will not detect your concealed gun.

Notice that they are not manned?

Their purpose is to prevent shoplifting. Certain store merchandise has RFID microchips imbedded in the packaging. When you pay for the item, the clerk deactivates these tags at the cash register. The "metal detectors" query the RFID chips as you walk through them. They can tell if you paid for the item. If not, a chime or some sort of sound is emitted, asking you to wait before leaving. A store employee may approach you to investigate.

So if you are not stealing stuff, you may ignore these things.