All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
In principle, an employer should trust his employees. He should also trust that they follow their consciences and values of honesty and mindfulness of Allaah; and Allaah is sufficient as Protector and Disposer of affairs. However, there is nothing wrong with an employer or someone who acts on his behalf conducting surprise inspections in order to check on the employees to make them alert and heedful of such inspection. The employer also has the right to install surveillance cameras in the workplace on condition that the purpose of installing them is merely to monitor the workflow and make sure that everything is running smoothly and efficiently. This is not considered spying on others as long as the employees are aware of the presence of these cameras. Rather, it is commendable of an employer to do so in order to shoulder his due responsibility towards his business and make sure that the work is running smoothly and so that he would thus feel at reassured. Moreover, installing cameras in workplaces and other places has many benefits and has become very common; you hardly find a place with no installed surveillance cameras either to monitor the employees or for security purposes and the like.
Allaah knows best.