The chemistry of a lithium battery leaves little room for error. In a crash, an electric vehicle becomes more than just twisted metal and broken glass. Power can vanish in a heartbeat. Fires can ignite. Sometimes, things blow up.
China’s national EV safety standards try to build in a buffer: battery packs must hold off on bursting into flames or blowing up for at least five minutes after a single cell overheats—a phenomenon known as thermal runaway. But those rules are calibrated to specific crash tests: frontal collisions at 50 kilometers per hour and side impacts at just 32 km/h. Real accidents, of course, often happen faster and hit harder. That five-minute window? It might shrink to seconds. And in that tight span, whether a door unlocks could spell the line between escape and catastrophe.
Which is why, deep inside the electronics of every EV, the door-locking system quietly plays the role of unsung hero.
First line of defense
Most cars on the market today use electronic locking. The setup makes remote unlocking and smartphone control easy. Once the car hits around 20–30 km/h, wheel speed sensors kick in and lock the doors by default.
Behind the scenes, it’s all run by the in-vehicle controller area network—a nervous system of sorts, where the battery acts as the heart. Thick, high-voltage wires (called hardwiring) carry power to the main controller. Secondary components, including door locks, communicate through finer CAN (controller area network) wires.
Some systems add redundancies—extra wiring, backup power sources—to make sure critical parts don’t fail if something goes wrong. But most of it still hinges on one thing: an intact battery.
In EVs, batteries are usually tucked behind the rear seats, away from typical crash zones. That placement, sandwiched between the B- and C-pillars, helps. But damage doesn’t always come through the front.
If the battery stays intact yet power still cuts off, odds are the wiring took the hit.
“Wiring practices are fairly mature in the industry,” one automotive R&D staffer told 36Kr. “We design them away from sharp metal, use rubber sleeves, that sort of thing. But materials make all the difference.”
There’s an entire ecosystem around wire protection: tape, heat-shrink tubing, corrugated tubes, spiral wraps. Prices run from tens to thousands of RMB, depending on durability and resistance to corrosion or vibration.
“Everyone uses protective layers. The question is what kind,” another engineer said. “Some companies are scaling back—cheaper materials, thinner wraps—just to save a few RMB.”
High-end international brands tend to err on the side of caution. Some local automakers? Not always.
And when the wires fail, so do the locks. They’re powered devices. No electricity means no function—unless they’ve been designed to unlock right before the power vanishes.
Second line of defense
This is a race against time—something the industry is familiar with. Look at airbags: crash sensors react in minute fractions of a second, triggering deployment just 20–30 milliseconds after impact.
But that kind of speed? It’s not standard for door locks.
Airbag systems often cost RMB 3,000–10,000 (USD 420–1,400), with premium sensors and fast processors baked in. Door-lock systems, by comparison, usually rely on slower, cheaper hardware.
“Even expensive cars might not have high-end safety features,” a supplier said. “Between different models—even within the same brand—there’s huge variation. Some look great, but cut corners where it really matters.”
Same wiring layout, but cheaper insulation. Emergency door systems that react slower. In today’s fierce price wars, saving pennies on components can cost lives when things go south.
Still, there’s movement. Some global brands are considering faster, premium sensors for door-unlock systems too, according to supply chain insiders.
And what about those polarizing hidden door handles? They have taken flak, but they are mostly cosmetic. Handles are just the interface. The real work happens at the latch, which is a time-tested mechanical mechanism.
As long as the lock disengages, the latch opens. The door swings out. Done.
Final line of defense
But what if power dies, locks stay shut, and doors jam?
“Mechanical systems are the last resort,” one functional safety engineer said. “Every car has to have a purely mechanical way out.”
US regulations spell this out: mechanical door-release systems are mandatory. China doesn’t explicitly require mechanical handles, but it does say doors must work in case of power failure.
“Automakers may vary in how they treat the other doors, but the driver’s side always has a mechanical handle,” the engineer added.
The problem is, those handles aren’t always where you’d expect. On some EVs, they are nestled next to the window buttons or hidden near the door pocket. “Why hide something that could save your life?” a veteran safety manager asked.
And this all assumes the door hasn’t warped from the crash. If it has, only cutting tools or rescue crews will get people out.
China is racing ahead on smart driving and active safety systems for EVs—measures meant to prevent crashes altogether. But when collisions do happen, battery fires can ignite and spread with alarming speed.
That’s where passive safety—like mechanical escapes and power-failure failsafes—becomes vital. Global joint-venture brands usually lead the charge here.
“At Mercedes-Benz, most passive safety testing is done through simulation,” one engineer said. “You can’t crash thousands of cars. But with years of data, we know exactly where to focus.”
Others in the supply chain echoed that view. “You can’t have it all. If you want top-tier safety and performance, the cost goes up,” one expert said. “Top brands build for safety first, then aesthetics or price. Some local makers don’t even know how to evaluate products holistically. They are too focused on flashy specs,” another added.
At the end of the day, there’s a brutal clarity to EV safety: when things go wrong, every millisecond counts. And sometimes, all it takes is a working door handle to tip the scales.
KrASIA Connection features translated and adapted content that was originally published by 36Kr. This article was written by Xu Caiyu for 36Kr.