a short term surveillance is possible against suspects and contact persons as an low-treshold measure (§ 161 StPO, procedural law).
a long-term surveillance (duration longer than 24hrs or to more than 2 days) is possible if other investigation measures not promising success (§ 163 f StPO). Only Offences of major importance (serious crime) justify the planned observation of a suspected person including the use of technical measures like GPS, cameras etc.(Art. 100 h) for a period up to three months.
The observation of other persons is permitted if it can be assumed that they are connected with the suspected person.
The term of limitation can be extended.
Tracking by technical instruments (§ 100h StPO) f.e. GPS-Tracker or IMSI-Catcher (§ 100i StPO) is possible in both cases