Is it permissible for the business owner to install surveillance cameras without the knowledge of his employees?
Question

Is it permissible for me, as a business owner, to install surveillance cameras, for two reasons: 1. To watch the progress of work and whether employees are doing their duties; 2. To detect instances of theft if it occurs, and to protect the shop from a security point of view. Is it permissible to install these cameras without the knowledge of the employees?
Praise be to Allah.It is permissible for the business owner to install surveillance cameras to keep an eye on the work of employees who are working for him, on condition that they are aware of the presence of cameras, so he will not see them in a state when their ‘awrah is uncovered or behaving in a manner he would only usually do when he thinks that no one is watching.
If the cameras are installed without their knowledge, this is the very essence of spying, which is prohibited according to the text in the Book of Allah (interpretation of the meaning):
{O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other} [al-Hujuraat 49:12].
And the Messenger of Allah (blessings and peace of Allah be upon him) said: “Beware of suspicion, for suspicion is the falsest of speech. Do not seek out one another’s faults; do not spy on one another; do not envy one another; do not turn away from one another; do not hate one another. Be, O slaves of Allah, brothers.” Narrated by al-Bukhaari (5144) and Muslim (2563).
Spying refers to seeking out people’s faults and shortcomings.
The interest that you seek to serve by installing the cameras, to keep an eye on employees and protect the establishment against thieves, may be achieved  properly by installing the cameras and informing the employees of their presence. Doing anything more than that comes under the heading of spying and seeking out people’s faults.
Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allah have mercy on him) said:
Spying means seeking out someone else’s faults, meaning that a person watches, listens attentively and eavesdrops in the hope of hearing something bad from his brother, or seeing something bad from his brother. What a person should do is turn away from seeking out people’s faults and not be keen to find out about them.… It is not appropriate for a person to spy on others; rather he should take people as they appear to be, so long as there is no circumstantial evidence to suggest anything to the contrary." (Tafseer Soorat al-Hujuraat  50, 51).
If there is a stern warning concerning the one who listens to people’s conversations when they do not want him to do so that he will have molten lead poured into his ears – as is  narrated in Saheeh al-Bukhaari (7024) – then what about the one who installs equipment to film the employee throughout his shift in the workplace, watching him in everything that he does and does not do so, and preserves this recording, and the employee may be on his own, or feel that he is shielded from people’s eyes, so he may do something that is not haraam in and of itself, and is not shameful if a person does it when he is on his own or with his family and children, but it is regarded as a  shameful and vulgar if he does it in front of people, then the business owner exploits this clip and threatens to circulate it and shame the employee, or blackmail him, and other kinds of mistreatment that are worse than simply listening to a conversation between two people who do not want to be overheard.
If the business owner would not like that for himself or for any of his children, then by the same token he must not like it for anyone else. The Prophet (blessings and peace of Allah be upon him) said: “Whoever would like to be delivered from Hell and enter Paradise, let him die believing in Allah and the Last Day, and let him treat people as he would like to be treated.” Narrated by Muslim (1844).
The one who thinks he is justified in spying on people and invents excuses for doing so is threatened with a punishment that fits his crime, which is that Allah will seek out his faults and expose him to shame, as is mentioned in the hadith of Ibn ‘Umar (may Allah be pleased with him), who said: The Messenger of Allah (blessings and peace of Allah be upon him) ascended the minbar and called out in a loud voice: “O you who have paid lip service to Islam but faith has not entered your hearts, do not harm Muslims or shame them or seek out their faults, for whoever seeks out the faults of his fellow Muslim, Allah will seek out his faults, and if Allah seeks out a person’s faults,  He will expose him even in the innermost part of his house.” Narrated by at-Tirmidhi (2032); classed as saheeh by al-Albaani.
And Allah knows best.