Observation without technical means is a practically relevant investigative tool in criminal proceedings, balancing the protection of fundamental rights and effective law enforcement. The legal basis for short-term observations is the minor investigative general clause of Sections 161 and 163 of the Code of Criminal Procedure (StPO). After a critical assessment of Section 163f StPO as a basis for long-term observations, 'otherwise significant' observation is identified as a third category. Special attention is also given to the legality of observations in specific contexts, such as preventive crime fighting or in cases of cumulative measures. The implications of the findings for similar covert actions, such as the use of undercover agents or informants, are also discussed.