@Tcof
Wait, they enter the room just like that all the time ? what about hentai set up ?
In all seriousness, I don't know if it's actually as prevalent as it makes it out to be, but I constantly see reference to video cameras or otherwise staff members having viewing access into rooms. Could technically listen in on the intercomm system in theory, too.
Apparently people renting karaoke rooms to bang got to be an issue. If the prices listed for love hotels are reflective, I can see why. It's a lot cheaper and apparently used to be very private. (And technically love hotels aren't supposed to get in anyone underaged. Although with so many seeming to be automated with regularly staff and customer never seeing one another that might not be much of an issue.)