A photocell is used to detect if rays of light fall into the can through micro-holes. Defective cans are automatically ejected at the outfeed conveyor after the Leak detector. A 100% quality-control ensures that only complete secure cans 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.