Drones have changed war. Small, cheap, and deadly robots buzz in the skies high above the world’s battlefields, taking pictures and dropping explosives. They’re hard to counter. ZeroMark, a defense startup based in the United States, thinks it has a solution. It wants to turn the rifles of frontline soldiers into “handheld Iron Domes.”

The idea is simple: Make it easier to shoot a drone out of the sky with a bullet. The problem is that drones are fast and maneuverable, making them hard for even a skilled marksman to hit. ZeroMark’s system would add aim assistance to existing rifles, ostensibly helping soldiers put a bullet in just the right place.

“We’re mostly a software company,” ZeroMark CEO Joel Anderson tells WIRED. He says that the way it works is by placing a sensor on the rail mount at the front of a rifle, the same place you might put a scope. The sensor interacts with an actuator either in the stock or the foregrip of the rifle that makes adjustments to the soldier’s aim while they’re pointing the rifle at a target.

A soldier beset by a drone would point their rifle at the target, turn on the system, and let the actuators solidify their aim before pulling the trigger. “So there’s a machine perception, computer vision component. We use lidar and electro-optical sensors to detect drones, classify them, and determine what they’re doing,” Anderson says. “The part that is ballistics is actually quite trivial … It’s numerical regression, it’s ballistic physics.”

According to Anderson, ZeroMarks’ system is able to do things a human can’t. “For them to be able to calculate things like the bullet drop and trajectory and windage … It’s a very difficult thing to do for a person, but for a computer, it’s pretty easy,” he says. “And so we predetermined where the shot needs to land so that when they pull the trigger, it’s going to have a high likelihood of intersecting the path of the drone.”

ZeroMark makes a tantalizing pitch—one so attractive that venture capital firm Andreesen Horowitz invested $7 million in the project. The reasons why are obvious for anyone paying attention to modern war. Cheap and deadly flying robots define the conflict between Russia and Ukraine. Every month, both sides send thousands of small drones to drop explosives, take pictures, and generate propaganda.

With the world’s militaries looking for a way to fight back, counter-drone systems are a growth industry. There are hundreds of solutions, many of them not worth the PowerPoint slide they’re pitched from.

Can a machine-learning aim-assist system like what ZeroMark is pitching work? It remains to be seen. According to Anderson, ZeroMark isn’t on the battlefield anywhere, but the company has “partners in Ukraine that are doing evaluations. We’re hoping to change that by the end of the summer.”

There’s good reason to be skeptical. “I’d love a demonstration. If it works, show us. Till that happens, there are a lot of question marks around a technology like this,” Arthur Holland Michel, a counter-drone expert and senior fellow at the Carnegie Council for Ethics in International Affairs, tells WIRED. “There’s the question of the inherent unpredictability and brittleness of machine-learning-based systems that are trained on data that is, at best, only a small slice of what the system is likely to encounter in the field.”

Anderson says that ZeroMark’s training data is built from “a variety of videos and drone behaviors that have been synthesized into different kinds of data sets and structures. But it’s mostly empirical information that’s coming out of places like Ukraine.”

Michel also contends that the physics, which Anderson says are simple, are actually quite hard. ZeroMark’s pitch is that it will help soldiers knock a fast-moving object out of the sky with a bullet. “And that is very difficult,” Michel says. “It’s a very difficult equation. People have been trying to shoot drones out of the sky [for] as long as there have been drones in the sky. And it’s difficult, even when you have a drone that is not trying to avoid small arms fire.”

That doesn’t mean ZeroMark doesn’t work—just that it’s good to remain skeptical in the face of bold claims from a new company promising to save lives. “The only truly trustworthy metric of whether a counter-drone system works is if it gets used widely in the field—if militaries don’t just buy three of them, they buy thousands of them,” Michel says. “Until the Pentagon buys 10,000, or 5,000, or even 1,000, it’s hard to say, and a little skepticism is very much merited.”