I've wondered about that myself - I actually asked one of the mpas about that and I was told that the girls were advised that it was a "fancy machine for sex toys" - apparently that is a touch screen where you can select butt plugs, handcuffs, didos, feathers etc for whatever fantasy you may have and then the box looking cabinets you see near the sinks across the room open with the item.
At first I thought cool, they are being innovative! But 12 months later its still a glass wall that looks tinted - very suspicious!!
Alex the owner at AGS was caught not to long (according to a post) for installing smart light bulb cameras in his rooms, so I wouldn't be surprised. If guys are recoding, I am sure that some spas have found a way to record us and watch the girls as well!
Maybe next time I'll act shady, pretend like I'm hiding a camera in the corner and see if when the mpa walks in she checks for it