In general, your employer is not allowed to monitor you to ensure that your work is running smoothly at the workplace. However, if there is a disruption to the work process, they have the right to get to the bottom of the causes. Particularly in the case of theft or the disclosure of business secrets, the employer is legally permitted in principle to monitor you. It is always important that monitoring or surveillance measures are proportionate. This is only the case if the employer's interests outweigh the employee's personal rights.