Keyless entry cars are convenient—but thieves can steal them in under a minute using cheap devices that capture your key fob’s signal from outside your home. It’s called a relay attack, and it’s on the rise.

The low-tech fix? Wrap your key fob in aluminum foil or store it in a Faraday pouch to block the signal. Also, keep keys away from doors and windows, and consider a steering wheel lock.

In the age of high-tech theft, a simple sheet of foil could save your car.