The invention concerns a detection method for checking sealed product packages for leaks, characterised in that it comprises the following steps: at least one previously sealed product (2) is placed in an air, nitrogen, or oxygen atmosphere, in a chamber (3) (step 101), the pressure in the chamber (3) is lowered to a secondary vacuum pressure below 10−1 mbar and, while continuing the secondary vacuum pumping of the chamber (3), the gases contained in the chamber are ionised to monitor the change in the chamber (3) of the concentration of at least one gaseous species of the gas volume contained within the sealed product (2) chosen from among nitrogen, oxygen, or argon, by analysis by optical emission or mass spectrometry (step 102).