[hjanssen]

No, not if you are not working in a bank where there is a specific reason for your employer which is for example exposure to a considerable risk of being robbed. It is also permitted if you have had problems in the past with employees stealing things from the company, but only in places where it makes sense and is proportionate.

In any case, you have to make that absolutely clear to your employees. Any unanounced surveillance is a criminal offence here.