A photocell is used to detect if rays of light fall into the can or bottle through micro-holes. Defective cans or bottles are automatically ejected at the outfeed conveyor after the Leak detector. A 100% quality-control ensures that only complete secure packagings leave the line. The Leak detector can be placed on the outfeed conveyor of the Necking machine. Alternatively, it can be integrated as a stand-alone machine in the line.