Surveillance by a detective, including secret image recordings, is only permitted if there is concrete suspicion.
BAG 19.02.2015 - 8 AZR 1007/13
Both the commissioning of a detective and the secret recording of images to monitor an employee must be based on a suspicion based on concrete facts. It is not sufficient that the certificate of incapacity for work comes from different doctors, that the clinical picture changes or that a slipped disc was initially treated by a general practitioner. If the requirements for such a suspicion are not met, the monitoring constitutes an unlawful violation of the general right of personality, which can justify compensation for pain and suffering.