Yes, a working Faraday pouch can stop a relay attack on a keyless-entry car, because thieves can't relay a signal they can't reach. But not every pouch works, and they wear out, so the only way to know is to test yours on your own car.
New to Faraday bags? Start with what a Faraday bag is and how it works.
What is a relay attack?
Keyless-entry cars unlock and start when the fob is close enough. A relay attack fakes "close enough." One thief stands near your house with a device that picks up your fob's signal. That signal is passed to a second thief standing next to the car, who opens it and starts it. As What Car? put it, criminals use relay box equipment that can pick up the signal from the key fob while it's in the owner's home. CAR magazine notes thieves can do it in under a minute using little more than an amplifier and a laptop.
No broken window, no forced lock. To the car, the real key is right there.
How common is it? What testing found
In December 2016, the National Insurance Crime Bureau (NICB) got hold of a relay attack unit and tested it on 35 different makes and models over two weeks. According to NICB's results, the device opened 19 of the vehicles (54%) and started and drove away 18 (51%). NICB's comment: "Maybe they don't work on all makes and models, but certainly on enough that car thieves can target and steal them with relative ease."
That test is several years old, and some carmakers have since added defenses (see below). But plenty of cars from that era are still on the road.
Do Faraday pouches stop relay attacks?
Good ones do. When CAR magazine tested pouches by putting a fob inside, walking to the car and trying the doors and the start button, all the pouches they tested worked.
The catch is consistency. Thatcham Research, the UK vehicle security lab, said: "We have tested a few of the pouches and the ones we've assessed have worked, but we can't guarantee they all will." They flagged two problems:
- Wear. On cheaper pouches, the shielding mesh can be damaged by constantly taking keys in and out.
- Design. Some pouches have two pockets, and only one of them blocks signals.
Independent bag testing points the same way. A SANS Internet Storm Center test found a sealed bag blocked Wi-Fi, cellular and NFC but still let 125 kHz access cards be read. In short, don't assume. Test with the actual fob and the actual car.
How to test a key fob pouch
- Put the fob in the pouch (if it has two pockets, use the shielded one) and close it exactly as instructed.
- Walk up to the car with the pouch in your hand and pull the driver's door handle. It should stay locked.
- If you have a second key, unlock the car with it, get in with the pouched fob and press the start button. The car should say no key is detected.
- Take the fob out and repeat. The car should unlock and start. That confirms the test was fair.
- Repeat every month or two. CAR magazine's guide says pouch performance can reduce over time.
More on why pouches fail, with full home tests: why do Faraday bags stop working.
Other fixes that don't need a pouch
Motion-sensing ("sleeping") fobs
Some newer fobs shut off their signal when they sit still. Ford introduced one in Europe that deactivates when it hasn't been moved for more than 40 seconds, so a fob lying in a bowl by the door has nothing for a relay box to pick up. Check your owner's manual or ask the dealer whether your fob has this feature.
Turning off keyless entry
Some cars let you switch off passive keyless entry in the vehicle settings, the companion app, or with a button sequence on the fob. The method varies by make and model year, so look in your owner's manual under keyless or smart entry. You'll still be able to unlock with the button.
Distance and habits
- Don't keep fobs by the front door or on a hook near a wall that faces the driveway.
- Store spare fobs in a tested pouch or a metal box (test that too; see DIY Faraday bags and boxes).
- Follow NICB's basics: always lock the car, take garage door openers with you, and don't leave valuables in sight.
Physical layers
CAR magazine also suggests steering-wheel locks, driveway posts, motion-sensing lights and security cameras as extra layers. A visible wheel lock makes a quick relay theft less attractive.
Questions people ask
Do Faraday bags block key fob signals?
A working one does. With the fob sealed inside, the car shouldn't unlock or start. Test yours at the car door, because some pouches don't block as well as claimed.
Can thieves still steal a car with the key in a Faraday pouch?
A pouch stops relay attacks, which depend on reaching the fob's signal. It doesn't stop other theft methods, so locking the car and using physical deterrents still matter.
How do I test my key fob Faraday pouch?
Seal the fob in the pouch, walk to the car and pull the door handle. It should stay locked. Then take the fob out and confirm the car unlocks normally.
Does wrapping a key fob in foil work?
It can if the foil fully encloses the fob in several layers with no gaps, but it tears easily. Test it at the car door the same way you'd test a pouch.
Can I turn off keyless entry on my car?
Many cars allow it through vehicle settings, an app or a fob button sequence, and some newer fobs go to sleep when not moving. Check your owner's manual for your model.
Thieves aren't the only ones logging where your car goes. License plate cameras do it every day. Grab the free Flock Camera Field Guide, or find out if police have searched your plate with the Records Request Letter Pack.
This article is general information, not legal advice.
0 comments