Multiple light beam safety devices are used for access guarding at machines and systems. The required arrangement for these protective devices is described in the harmonized standard EN ISO 13855, which replaced the previous version EN 999 in 2010. As introduction of EN ISO 13855 has resulted in changes to details, the question repeatedly arises as to whether 2-beam safety light barriers can still be used on new machines. For existing machines, the question is whether 2-beam systems have to be replaced by 3-beam systems.