This method is used for sealed objects that cannot be connected directly to the detector (semiconductors, waterproof watches, etc.).
The part is placed in a chamber containing pressurized helium. The helium penetrates the part if it has a leak. The part is then removed from the chamber and placed in another vacuum chamber which is connected to the detector. The helium escapes from the part through the leak and produces a signal. This signal is not a direct measurement of the leak as the helium pressure inside the part is difficult to determine. Several parts play an important part such as: the pressurization time, the helium bombing pressure, the internal volume, the aeration time, the size of the leak.