To establish the integrity of a product located in a container a given feature of the product in the container is determined by means of a first measurement method in which a first physical property of the product is ascertained, the given feature is additionally ascertained at least directly or by means of a second measurement method which is based on a second physical property which is different from the first physical property, and the values obtained by means of the two measurement methods of the given feature are compared. If the product is a drink in a bottle and if the given feature is the fill level, the first measurement method can consist of the fill level being measured by means of absorption of an X-ray beam, and the second measurement method can consist of the change effected by the bottle in the resonant frequency of a high-frequency oscillating circuit being measured.