That actually could have been a great plot device. A device that detects Changelings. Likely initially developed by Dr. Mora Pol. Tucked away somewhere on the station found by Rom. Quark would have it for a while as he could use it to sweep the area and check for Odo (which would lead to it being an Odo detector). That’s how it would likely first be introduced. But soon, confiscated. Then its brought back and becomes more important once the Dominion plot really goes forward and they’re looking for ways to find Changelings.