Jtdcftul

In a story I'm working on, humanity had sometime in the past reached a very advanced technological level (far higher than ours), but then had a devastating global war, and afterwards technology had been banned.

Now at the time of my story, those events are long gone, and have passed into the realms of legends. All abilities that technology provided, as far as they are referenced in those legends, are ascribed to magic. The society that evolved is about medieval level.

However there are (very rare) occurrences where old “magical” (that is, technological) artifacts (mostly weapons) are found, some of which actually still functional (in particular, that happens to the protagonist).

Now later in the story it will be revealed that this magic is in fact ancient technology, but I'd like to foreshadow it from the very beginning.

So far I've described the magical (technological) artifact the protagonist found as shiny, and the effect of the artifact (which is causing hallucinations, making people fight against each other thinking they fight monsters) is triggered by some sort of knobs.

I also tried to hint at it with tales about what magic could do, but anything I can think of is stuff that's either unsurprising for magic, or so obviously technological that it wouldn't be foreshadowing any more.

Are there any other good ways to hint at magic actually being very advanced technology?

Magic vs advanced technology is a common enough question in fiction that your readers will already be primed to wonder. I agree with Amadeus that the reference to "knobs" is, in and of itself, enough to tip the reader off. Magic wands don't have buttons.

What you want though is not just the reader thinking advanced technology but considering where the tech comes from. Is it from an older society? aliens? a parallel but unknown community (like the fairy world in Artemis Fowl)?

So reference the "devastating global war." You might even talk about how someone invented something but it got taken away.

You don't need much here. Let the reader have the thrill of figuring it out.

The fact that you use "knobs" that turn is enough, in my opinion.

Another way would be to have a naturally scientific (logic based) mind actually fix an older artifact and get it working again. It would have to be a simple mechanical fix, but in the process of examining one of these found artifacts that doesn't work, she notices that a string (wire) looks broken.

It is just a minor power-supply problem, and though she doesn't understand electricity or anything else, she does understand medicine. She holds the two ends of the wire together and the device reacts: Lighting up intermittently, perhaps.

She does a better job of holding metal to metal, and the lights become constant. She decides to let the metal string "heal" by binding and gluing the broken ends together, metal to metal, and the device is operational.

She messes with the buttons and "magic" happens, like the stone in her fireplace slumps. It isn't a liquid, it isn't hot, but she can shape it or scoop it out like clay. Whatever. It stays that way. Until she presses the other button, then the shaped stone becomes just as solid as it was before.

To her, it is still magic, but to anybody reading this scene, that is unmistakably technology.

That might be too strong, but if so, I would also clue in to "tech" the moment I read "knobs". Knobs and buttons and such are mechanical, anything mechanical that performs a function screams "tech" to me.

And it isn't terrible for the reader to know something that none of the characters know; then part of the game is reading to see how and when the characters figure this out, and what it means about their history or origin. So there is still a mystery there.

How do you ban "technology"?

To ban something, they would first need to be able to identify it. They would need a pretext, however flimsy, for why these artifacts are banned. Someone knows what it is, or has a good enough idea how it works, to create a law and enforce it.

Human beings would not become so stupid as to "forget" what a metal is, or that knobs are mechanical creations. Even stone age people would know it didn't come out of a cow or a plant. Suppose they have lost the knowledge to smelt bronze, they would have soft metals like copper and gold. These metals could be scavenged from ruins, just as Egyptian tombs were scavenged for precious metals thousands of years after the society that created them were gone.

Clarke's Third Law

You have a MacGuffin that is controlling events in the story. It doesn't matter if it's magic or from outer space, that reveal isn't some "twist" to the plot. It is obviously foreign and anachronistic to the setting. This won't be a surprise to the reader, at no time will they assume it is just a magic pumpkin up until the reveal it has knobs and wires. It's Clarke's Third Law: Any sufficiently advanced technology is indistinguishable from magic. It makes no difference.

"Technology" is ridiculously broad. A society that banned all technology would ban farming and weaving. They would die because modern humans only evolved with the help of technology: stone blades, fire, and leather-working. Humans that keep livestock have rope tethers and fences. Without technology, humans are far too weak to hunt for meat, and without meat humans cannot support a calorie-hungry brain.

You have a world-breaking premise. Fix it with worldbuilding and characters

You have a world-breaking premise so fix it. SOMEONE knows what "technology" is, and they have enough of it to enforce that no one else has any. Your discovered artifact is taboo, evil, ungodly – all the scriptures say so. These artifacts were once everywhere and they poisoned the people until the Praetors® were established to rid the land of these horrible things. Now we live free from the evil, but if you see an artifact you must tell an elder who will contact the Praetors® to come and cleanse the land. This gives you an antagonist.

Someone has found the artifact, and of course it is an artifact what else could it be? But the person who found it is not always someone who follows the rules. Maybe they are greedy and believe the artifact will make them rich. Maybe they came from a village that was "cleansed" by the Praetors. Maybe there are rumors that the artifacts can heal sickness and disease. Maybe the village well has become polluted with human waste, and the artifact gets dropped into the well to purify the water, it kills the microbes but eventually poisons the village. The point is you need a protagonist who believes they are doing the right thing by keeping the MacGuffin from the antagonist.

The conflict needs to be between characters who have mutually exclusive goals.

Don't give an inanimate object all the stakes in your story. The only way to raise the stakes for an inanimate object is to reveal its origin or to increase its power, presumably things you plan to happen anyway. There is no internal conflict or decision to be made. There is no "twist" to reveal – again, Clark's 3rd Law says the distinction between magic and technology in this scenario is meaningless. Withholding this information doesn't raise the stakes. It might be a curiosity for the reader, but it doesn't change anything for the characters.

MacGuffin's aren't characters. They get a special word because they aren't meant to be examined up close (the origin is a box with nothing in it). MacGuffins tend to fall apart when taken too literally. Instead MacGuffins are elusive and mysterious. You have a taboo object which is banned. Maybe your protagonist isn't comfortable looking at it directly. Maybe it is scary to contemplate so many unanswered questions that go against the scriptures. Maybe it's kept wrapped up and hidden, so those knobs and wires aren't so obvious. Think about it – if you found a demon's head in the woods, would you bring it home and prop it up on the mantle, or would you keep it hidden in a box in the garage?

Don't rely on this "reveal", it can only feel important if it somehow changes things for the characters. Instead you can describe its "strangeness", emphasizing how it makes them feel (frightened, ashamed, greedy). None of the characters would give such a loaded object neutral descriptions. In addition, the various opinions would escalate as the artifact's influence spreads, creating division as everyone sees it as something different, filtered through their fears and biases. If it was sinister before, it becomes menacingly evil. If it seemed like an opportunity for profit, it will shine like gold. There should be no neutral or objective description of the object. The reader is never sure what it is. The important thing is what it represents, and how each character reacts.