SKG is an independent testing institute, which sees to it that security products comply with the NEN5089 standard for strength and durability. Products which comply to this standard are regularly tested to ensure that the products continually comply with this standard.
If a product complies with the requirements, it receives a classification in stars. There are three different classifications:
| 1 SKG star : standard burglary resistant | |
| 2 SKG stars : heavy burglary resistant | |
| 3 SKG stars : extra heavy burglary resistant |