Basically, having someone act as a courier for a book/manual/whatever for an evil warlord in the zombie apocalypse. He opens it, and realizes that it's something that can help weaponize zombies, perhaps by controlling them. Just looking for ways in which this might be done. Obviously, it's fictional, but looking for something that doesn't take people out of their suspension of disbelief.
Computer chip in the brain (something like Musk's Neuralink maybe) that connects to the nervous system and can control the muscles. With a remote control of some kind. Magic Hypnosis, in which it's discovered that much of the zombies' brains remain functional, but are simply not being used, or have been overtaken entirely by the hunger for flesh. The hypnosis enables it and puts it under the control of the hypnotist. Hey, they weren't using it! This could be a big metaphor for cultism or widespread manipulation like propaganda. Maybe to hypnotize them he makes them all watch TV (his special programming of course). Maybe he just replaces the hunger for flesh with some other basic drive. Drugs. I leave the mechanism to someone else to figure out.
Pavlovian conditioning. Change the zombie creation from undead, to a bio weapon, rabies variant. What level of control are we talking about? If it is simply directing them to a target, then a drone with lights and sound would draw them. If you are talking about a level of control where they could be used as a domestic servant, then you are getting into magic.
Well, modern zombies are derived from the Haitian voudou tradition, and ultimately from West African folklore, so depending on your story's tone maybe you could find some inspiration from there. https://www.npr.org/sections/codeswitch/2013/12/13/250844800/zoinks-tracing-the-history-of-zombie-from-haiti-to-the-cdc
You might decide to use the literary device of an Achilles' heel - There is a wonderful chart at the link below detailing all the Achilles heels of a vary array of superheroes https://www.morphsuits.com/blog/the-achilles-heel-of-superheroes-and-villains/#:~:text=Faster%20than%20a%20speeding%20bullet,character%20with%20a%20significant%20weakness.
Control where they go, and who they attack. Pretty much the most valuable weapon one could have in the zombie apocalypse, so I want it to be something that's not obvious/easy, like Pavlovian conditioning. Funny you mention that, though. This is for a screenplay, and my opening line is literally: OVER BLACK: Sounds of a ZOMBIE SNAPPING AND SNARLING. We hear the spit sloshing around its mouth, a Pavlovian response to the scent of HUMAN FLESH. I thought about drugs, but I also forgot to mention it's a screenplay. The method of controlling the zombies is something that is only shown briefly, but I want the viewer to immediately understand it. And my main character is kinda an idiot, so I want him to be able to put the puzzle pieces together, too.
Pheromones. Spray them in the air to elicit a particular response from the zombies. One for feeding, one to make them docile. Spray it over someone to make them the target.
In that case there could just be a brief montage showing the villain (or whoever it is) doing some simple operation on their brains (or working some voodoo mumbo-jumbo, or spraying some chemical) and then the zombies obey. Maybe viewers don't even need to understand the specific mechanism for it. Zombie movies and stories are basically magic, often disguised loosely as vague science, because if you examine it closely, it makes no sense that the dead can walk around or do anything.
In most zombie stories, they blindly travel towards sound. I imagine a drone could lure them around. You’d probably not be able to get them very far as they walk slow and drones drain batteries quickly. But they’re propellers make sounds in frequencies human ears are very sensitive to. If you could find a way to walk among them, you could probably just influence them with your own movements. If one goes off in a direction with purpose, others tend to follow. In the walking dead being covered in human remains made the zombies think you were one of them and could move them around.
The fool triumphant is a fun genre when done well. I might also suggest John Ringo's under a graveyard sky. His is a different take on the Zombie genre that works well. I particularly liked his central park scene. Some interesting psychology there.
Those aren't bad ideas at all, but the problem I'm having is that I need something that, chances are, most people wouldn't think of, or didn't know how to do. Like, I'm sure someone could definitely think to use sounds to draw zombies to an area. However, I'm looking for some sort of technology, device, or something that could give whoever holds it ultimate power -- the power to control zombies. If it's something that others could easily think of or implement, it wouldn't necessarily be all that valuable. As of now, I'm going with schematics for a chip implant in the brain because the bIg sEcReT wEaPoN, but not sure if that's good enough.
The second episode of the old Night Stalker TV series had a zombie controlled by an old voodoo priestess. She wrote the victim's name in chicken blood on a tiny coffin, and worked a spell to activate the zombie. If you can find it, the episode is one of the best of that show, particularly where Kolchak is lying beside the dormant zombie, getting ready to sew it's lips shut around salt. Then the zombie opens it's eyes...
There's also a pretty wild sequence in the movie I Walked With a Zombie showing one means of controlling a zombie. I wonder if that segment is on Youtube? Can't find that part specifically, but it leads directly up to this scene: The blonde woman is the zombie (supermodel zombie apparently), the dancing and drumming is going on, and the man is drawing a voodoo doll of her toward him little by little on a string, which irresistably draws her to the ritual. Her nurse follows. This is Haitian zombies (the original kind), so they're not really dead bodies, more like people that have had a hex put on them and act like the living dead, though some do seem more dead than others.
What about some Bluetooth headphones? If you could connect some to a single zombie, perhaps you could use 3D sound to lure it around without making an audible noise that other people can hear. If you can direct one of them and get the others to follow it you don’t need a whole lot. you’d have to give them some sort of feedback to get them to do anything. If they respond to touch, perhaps a Pavlovian response to a shock collar could train them to do certain tasks.
In Z Nation, the character who received the vaccine can mind control zombies. I wouldn't copy that directly, but there may be something in it. What if the mechanism were sonic? Maybe the villain has a device that emits various frequencies that the Z's respond to. It could even be hidden in another transmission so the living can't hear it. Raising and lowering pitch could steer them like remote control cars, if you want, or simply give attack/don't attack signals.
