As do doors that automatically pop open as you approach.
I had to explain to my daughters that this was unavailable at the time, and they had to have a crew member push a button as the actor approached. There are out-takes on YOutube where the timing gets off and Spock walks right into the door.
And less than 10 years later, they existed. I remember doors that opened for me as a kid - and that would have been early-to-mid-1970s.
One of the apocryphal tales from the set is that some tech guy and said that automatic was the hardest Trek gadget to accomplish in the real world. Heard that tale in multiple interviews with cast members but never any real proof, it’s funny of course because it was the first one that made the jump.
They were widely available, just not on the set.
“Electric eye” is an old-fashioned term for a photodetector, an electronic circuit activated by light. First developed in the 1890s, this concept has been adapted to new devices and technology and is still in use in the 21st century. Common applications include remote controls, automatic doors, and motion detectors. This particular term has gradually faded from use at the end of the 20th century, although it was revived in 2009 to describe advances in artificial sight. ...
... The once-novel electric eye had become a commonplace device by the last third of the 20th century. Familiar uses included automated doors in supermarkets and other public buildings
More here
It was even more low-tech than that, from what I've read. A couple of guys behind the wall just pulled the doors open by hand.