Interesting topic here
I can't tell for electronics or other labs, but as for office workers (I'm a project manager) there are written rules you have to sign when you sign your contract:
1. You are not allowed to use office equipment (PC, cell phone, etc.) for private, non-work-related tasks
2. You are not allowed to use private equipment for your work (other country organisations have things like BYOD, but that was deemed unsuitable for Germany)
3. You have to check in to the time tracking system when you arrive at the office and check out when you leave
4. You are not allowed to stay in the office (or even the building) once you have checked out. You have to leave immediately and go home
So much for office work in Germany. (at least in the companies I know so far)
I'm pretty sure you'd be sued to hell and back if you tried to use the lab for private projects, not to speak of other customer's projects, even if they are unrelated to your company's business...