Yes, the work of private detective agencies is completely legal and there is no illegality involved in it. Currently, there is no law to regulate private detective agencies in India, unlike. The security agencies, where one need license to open up a security agency. As there is no law which restricts the working of private detective agency, any person who wants to work as a private detective is free to do so. Now, the big question is the means to which private detective agency will resort to collect information. The detective Agency shall not resort to any illegal means to retrieve information. Suppose to lady come up with a query that her husband talks over phone and she wants to know with whom, he speaks now, in this particular case, one method is to retrieve call details by bribing police officials. The second method is selling a spy gadgets which can record the conversation. The first method is illegal and second is legal.