Everyone judges the plausibility of a movie through a different lens. If you're a doctor, you may think: “That character would not have survived that fall.” If you're an astrophysicist: “That's not how black holes work.” And if you're me, it's more like: “What a dumb concept of future personal technology!”

It makes me crazy when sci-fi moviemakers dream up stuff with no basis in science. Human teleporters? Sorry, Star Trek. A bed that detects and cures cancer in seconds? No, Elysium.

On the other hand, some movies depict futuristic technologies that are so plausible and practical, people invent them in the real world. Star Trek's self-opening doors are now a standard feature of grocery store entrances, and the driverless cars from Total Recall (and many other movies) are already on American roads.

Lately it's clear that Hollywood's production designers have been putting serious thought into the tech we'll someday carry. Her, for example, is about a man who falls in love with his Siri-like voice assistant. He talks to her through a single earbud, through which he gets a surprising amount done: processing e-mail, flipping through news stories, sending messages. When an image is essential to the communication, he flips open his phone, where the picture appears.

This solution makes a lot of sense—more than, for example, Google Glass, a now discontinued headband that placed a miniature screen above your eyebrow. Social missteps, not technical ones, hastened its demise: Glass's camera intimidated others and made you look like an obnoxious cyborg. The Her earpiece delivers many of the same benefits, albeit discreetly and comfortably.

My only beef with Her is that nobody ever precedes a command with, say, “Alexa” or “Hey, Siri.” How do the movie's computers know when you're speaking to them? Otherwise, Her nails it in the plausibility department. Already Apple's AirPods and Google's Pixel Buds let you converse with your voice assistant in much the same way, although at this point, you're more likely to receive news and weather than love and fulfillment.

In a recent Netflix movie called What Happened to Monday, humans live in a dystopian future where, to control overpopulation, it's illegal to have more than one child. The characters wear wristbands containing tiny projectors. They shine perfectly crisp, color images onto their palms, which the characters tap as though they are touch screens. I'll bet the screenwriters were inspired by a viral 2014 video about a slim wristband called the Cicret. (It raised more than $500,000 from individual backers before being debunked as wishful thinking.)

You can see why people went nuts over the concept: imagine having all the power of a smartphone without actually needing a smartphone. We won't see this in the real world, though. Even if a pico projector, battery and processor could be shrunk and squeezed into a thin band, insurmountable challenges remain. How would the projector attain sharp focus on an irregular, moving palm? How would it project enough light on sunny days? How would it work on very light or very dark skin? Above all, how would multitouch gestures work, when any finger in the projector's beam would cast a black shadow over the rest of the “screen”?

The robots in HBO's Westworld—so sophisticated that they are indistinguishable from humans—might be a bit of a stretch. Yet the personal tech in that series makes a lot of sense: the characters carry cardboard-thin, trifold phones. When you need a quick check, you glance at its “cover”; when you need the bigger picture, you unfold it into a tablet.

Most of these shows, however, continue to get one thing absurdly wrong: apparently, in the future, our computers make little chirps and beeps as their text and images appear. Why do moviemakers think that adding silly sound effects make their futuristic machines more rather than less plausible? In the real world, a room full of burbling screens makes us crazy.

Well, I suppose I should let that part go. They're just movies, right? They're not a depiction of the future—at least not yet.