It is to install spy software on someone’s PC without their knowledge if you do not own the device or lack legal authority (e.g., spying on a spouse’s personal computer can violate wiretapping laws).

Often permitted in common areas (sinks, lobbies) for security, but recording in private stalls is illegal in many jurisdictions. Requirement:

There is that is both effective and legal for unauthorized surveillance. If you see a product making that claim, it’s either a scam, malware, or both.