Car thefts have been on the rise for five years, and modern security systems aren’t stopping thieves. But there’s a simple trick that can keep your car right where you parked it. And it doesn’t require an expensive alarm or fancy tracking device. According to experienced mechanic Scotty Kilmer, all you need is about ten seconds and access to the fuse box under your hood–and the relays there.

A cheap and easy anti-theft trick

New cars are loaded with computers, but sometimes the best solution is an old-school, hands-on approach. As Kilmer explains, “A cheap and easy way for any old or new car? Just take out any important relay.”

Most cars have an easily accessible fuse box under the hood or inside the cabin. Inside, you’ll find relays that control key systems—like the ignition or fuel injection. If you remove the right relay, the car won’t start, no matter how skilled the thief is.

“You really don’t want your car stolen? You just pop the hood, zoom in here, and just pull it up,” Kilmer says. He recommends targeting the fuel injection or ignition relay: “If you pull it up, they’re never going to get the car going.”

I’ll add that the ignition relay will prevent them from even starting the car. But the fuel pump relay will also keep them from getting away and may make it much harder for them to figure out what is going on.

Unlike a kill switch, which can be found and flipped back on, a missing relay is a problem for thieves. “Odds against a thief having a fuel injection or an ignition system relay for your car lying around? Not slim to none,” Kilmer adds. The relay is a box about twice the size of a box of matches, so you can just take it with you and reinstall it when you return.

How to use the relay trick

The process is simple. Find your fuse box (check the owner’s manual if needed). Look for a diagram on the cover or inside the box—it will label the relays. Identify the fuel injection or ignition relay and pull it straight out. There may be a plastic tab on one side you need to wiggle to remove it. Then, store it somewhere safe, like your pocket or backpack.

“When you want it to run, you just plug it back in, put the top back on, very simple and easy to do,” Kilmer says.

This trick works because it makes stealing your car too much hassle. “The whole thing about having your car stolen is you want to make it the most work possible for anyone to steal,” Kilmer explains.

Is removing a relay better than modern security?

New cars have high-tech immobilizers and keyless entry systems, but they’re not foolproof. Thieves are using scanners and key programmers to bypass them. A relay trick, though? That’s old-school and effective. Combining the relay trick and modern anti-theft tech is a smart strategy.

“It doesn’t matter what kind of computers they have to try to start your car, without that relay, the vehicle is not going to start,” Kilmer says. So if you’re looking for a simple, free way to make your car theft-proof, start by going under the hood. You can see Kilmer show this trick himself in the video embedded below: