Illustration of a relay attack between a key fob and a car

RFID blocking, explained: keyless car theft and relay attacks

Answer Summary

Keyless car theft works by relaying the signal from your key fob — even while it sits on a table inside your home. Blocking that signal stops the attack. The same principle protects contactless cards and passports. Here's what a relay attack is, and how signal-blocking storage prevents it.

Key Takeaways

A relay attack depends on your fob being reachable. One radio picks up its signal through a wall or a door; a second radio replays it beside the car.

Nothing is broken and nothing is forced. The car simply believes you are standing there.

Put the fob inside a conductive, signal-blocking enclosure and the chain breaks at the first link: no signal out, no relay in.

The same shielding keeps contactless bank cards and modern passports quiet until you take them out.

A flat diagram of two car key fobs inside a pouch on the left and a car at a distance on the right, its signal arcs stopping well short of the pouch.

Keyless car theft works by relaying the signal from your key fob — even while it sits on a table inside your home. Blocking that signal stops the attack. The same principle protects contactless cards and passports. Here's what a relay attack is, and how signal-blocking storage prevents it.

What a relay attack is

A keyless car unlocks when it senses its fob nearby. Thieves turn that convenience against you with two small radios. One person stands near your house and picks up the faint signal your fob is always broadcasting — through a wall, through a door, while the fob sits in a bowl by the entrance. That signal is relayed to a second device held next to the car. The car is fooled into thinking the key is right there, and it opens. No broken window, no forced lock — the car simply believes you're present.

How blocking the signal stops it

The whole attack depends on the fob's signal being reachable. Put the fob inside a conductive, signal-blocking enclosure and there's nothing to relay — the chain breaks at the very first link. A signal-blocking pouch or box for your keys by the door is one of the simplest ways to shut this down: no signal out, no relay in. It costs you nothing but the second it takes to drop your keys in the box.

Wallets and passports, too

The same shielding protects contactless bank cards and modern passports, which carry RFID and NFC chips a reader can wake from a short distance. A signal-blocking wallet or sleeve keeps them quiet until you take them out to use them. A secondary case next to car keys — but a real one.

The same principle, for your phone

A Faraday-lined box does for a phone exactly what a fob pouch does for a car key: it stops the signal at the wall of the box, so the phone is unreachable until you open it. Same physics, pointed at a different kind of quiet — not protecting your car, but protecting your attention.

See the principle at work in the Stolp × Marie Kondo box, and the rest of the Faraday / Signal-Blocking collection.
R Blank
Written by R Blank Founder & CEO of Shield Your Body, author of Empowered, and host of The Healthier Tech Podcast

R Blank is the founder of Shield Your Body and the author of Empowered: A Practical Guide to Protecting Yourself from EMF. He spent years thinking about the devices we keep closest, and what they quietly ask of us in return. Then he put his own phone down, and found clarity, stillness, and the sense of being present in his own life again on the other side. In 2024 he brought Bagby into the Shield Your Body family, to help more people find their way back to the same.

FAQ

Frequently asked questions

How does keyless car theft actually work?

A relay attack uses two radios: one picks up the signal from your key fob through walls, even while the fob sits on your table at home. That signal is relayed to a second device near your car, which makes the car think the key is present. No forced entry—the car just unlocks.

Can relay attacks really work through walls?

Yes. Key fobs transmit a short-distance radio signal that travels through walls and windows. That's what makes a relay attack possible—the attacker doesn't need line of sight, just to be within range.

What's RFID and NFC, and why do they need blocking?

RFID and NFC are short-range radio protocols that let devices communicate wirelessly—key fobs, contactless credit cards, passports, some ID cards. A reader can wake these chips from several feet away. Blocking the signal stops the reader from reaching them.

How does signal blocking stop a relay attack?

Put the key fob in a conductive, signal-blocking enclosure, and there's nothing to relay. The first radio picks up nothing; the chain breaks at the first link. The same principle protects your wallet or passport.

Do I need signal blocking for my car key?

If your car has keyless entry (push-button start), a relay attack is possible. A signal-blocking pouch or box stops that attack. Whether you need one depends on your car model and local theft patterns.

Is this the same principle as the Stolp box for phones?

Exactly. A Faraday-lined enclosure stops wireless signal at the wall, making whatever's inside unreachable. For a car key, blocking stops theft. For a phone, blocking enables true disconnection—yours to control, yours to open.