Does a faraday bag actually stop keyless car theft?

It stops the relay attack specifically - the one where thieves capture your fob's signal near the house and repeat it to the car. Sealed in a working faraday bag, the fob can't respond to the car's query, so there's nothing for the relay to forward. It does nothing against theft methods that don't involve your key signal, like a broken window or a flatbed tow, so treat it as one cheap fix for one common attack rather than complete protection.

Will a faraday bag damage my key fob or drain the battery?

No. The bag blocks radio signals in and out; it doesn't put any load on the fob. If anything a fob that isn't constantly waking to answer your car may see slightly less battery drain. There's nothing magnetic in these pouches that would harm the electronics.

Can I just use aluminium foil, a metal tin, or the microwave instead?

These are the classic improvised versions and they can reduce the signal, but none of them is reliable. Foil tears and stops sealing, a tin usually has a seam or a lid gap that leaks, and a microwave is designed to contain one specific frequency, not the range a fob and its relay use. They also all fail silently - you won't know it stopped working. If you try one anyway, run the same walk-up-to-your-car test, and re-run it often.

My car has a motion-sensing fob that goes to sleep. Do I still need a bag?

Some manufacturers now ship fobs that stop transmitting once they've been still for a while, which does close the overnight relay window. Ford's motion-sensing key fob is the clearest published example: Ford says it sleeps after 40 seconds without movement and won't respond to a relay attempt until it's picked up again. Two caveats. It only helps once the fob has actually been sitting still that long - a fob in a coat pocket by the door that gets knocked as people pass may keep waking. And it does nothing for a spare fob that's an older model without the feature. Check your owner's manual for whether yours has it; a bag is a few dollars and covers the case where it doesn't.

How do I know my faraday bag still works?

Test it, and keep testing it. Seal the fob, walk to the car, and try the handle and then the ignition. If either responds, the bag isn't sealing. Do this the day it arrives, with each fob separately, and again every few months - the conductive fabric wears with repeated folding, and a bag used daily for a year is not in the condition it shipped in.

Buying guide Updated 2026

The Best Faraday Bags for Key Fobs

A faraday bag is the one cheap thing that reliably stops a relay attack, where thieves stand near your front door, pick up your key fob's signal, and repeat it to your car. For most people the answer is the Lanpard two-pack - one bag for the daily fob, one for the spare that's been in a kitchen drawer for years. If your fob is large or you want a roomier, better-documented pouch, the DefenderShield Ultra Armor bag has a bigger interior. Picks updated September 2026, when the long-time favourites from Mission Darkness and SLNT were both out of stock on Amazon.

At a glance - 2 faraday key fob bags compared

Bag	Best for	Approx. price	Interior size / closure
Lanpard Faraday Bag for Key Fob (2-Pack) Check price	Best for most people - two bags, covers the spare	Check current price	About 3.15 x 4.5 in; snap closure
DefenderShield Ultra Armor Key Fob Faraday Bag Check price	Best for large fobs - roomier single pouch	Check current price	5.5 x 3 in; VELCRO closure

What a faraday bag actually stops

A faraday bag is a pouch lined with conductive fabric that blocks radio signals from reaching or leaving whatever is inside it. For a car key that matters because a proximity fob is always listening: it broadcasts and responds whenever your car asks, even from a hook by the door. In a relay attack, one thief stands near the house with a device that picks up the fob's signal and a second stands at the car repeating it, so the car believes the key is in the driver's hand. Sealing the fob in a faraday bag breaks that chain at the source - the fob can't answer, so there's nothing to relay. It does nothing against a smashed window or a tow truck, and it doesn't need to; it solves one specific problem cheaply. We cover the attack itself in more detail in our guide to faraday pouches and relay theft.

How to choose

Measure your fob first. This is the mistake people actually make. The Lanpard pouch is compact at about 3.15 x 4.5 in, and the DefenderShield has 5.5 x 3 in of interior. A large proximity fob, or a fob on a bulky keyring with a bottle opener and three house keys, may not sit far enough inside a small pouch for the closure to seal.
Buy two, not one. The spare fob in a drawer is just as relayable as the one in your pocket, and it's the one nobody thinks about. This is the main reason a two-pack is the pick for most people rather than a single premium bag.
Closure style is what you live with. The Lanpard bag closes with a snap; the DefenderShield uses a VELCRO strip. Both work, but a closure you find fiddly is a closure you'll stop using, and a bag you don't use protects nothing.
Ignore dB figures you can't check. Shielding numbers are quoted freely across this category and there's no independent testing behind most of them. DefenderShield publishes a shielding range; Lanpard publishes no lab figures at all, and its track record is reviewer walk-up tests. The practical check that matters is the one you can run yourself - see below.

Test the bag yourself when it arrives - it takes a minute

Don't take any shielding claim on trust, including the ones on this page. Seal your fob in the bag, walk up to your car with it, and try the door handle the way you normally would. Then, still with the fob sealed, try to start the car. If either works, the bag isn't sealing - usually because the fob is too big for the pouch or the flap wasn't folded far enough over. Repeat the test with the spare fob, since the two are often different sizes. Re-run it every few months: the fabric in these bags wears with use, and a bag that's been opened and closed daily for a year is not the bag you tested when it arrived.

Why there's no faraday box pick here

A faraday box - a lined tin or case for the hallway table - is a genuinely good idea, and it's the format most people ask about. We're not recommending one. Search results for them are almost entirely unbranded marketplace listings with no manufacturer behind them, no published shielding specification, and no way to check that the product shipping today is the one that was reviewed a year ago. We'd rather leave a gap than point you at a box we can't stand behind. If you want a box, the honest version of that advice is to test it the same way as a bag the day it arrives, and to treat the listing's dB claims as marketing. A bag you've actually tested beats a box you haven't.

A note on Mission Darkness and SLNT

If you read around this category you'll see Mission Darkness and SLNT (formerly Silent Pocket) recommended often, and both publish real lab-test standards for their fabric. We haven't listed either as a pick because every key fob listing we checked for both brands on Amazon in September 2026 was out of stock, and we're not going to send you to a page you can't buy from. If they come back in stock, we'll look at them again.

The picks

Best for most people

1. Lanpard Faraday Bag for Key Fob (2-Pack)

$11.69 as of Oct 12, 2026 09:00 UTC

A two-pack is the right shape for this problem, because almost everyone has a spare fob sitting in a drawer that's just as exposed as the one in their pocket. Lanpard's pouch is a carbon-fiber-look PU shell over a double layer of RF shielding cloth, closed with a snap, and compact at about 3.15 x 4.5 in. It's an Amazon-only brand with no published lab testing, which is why the walk-up test below matters more here than with a premium bag - but it is one of the most-reviewed key fob pouches on Amazon, and reviewers consistently report that a sealed fob stops opening the car. The common complaints are fit (large or multi-button fobs are snug) and the need to close it fully every time.

Pros

Two bags, so the spare fob is covered too - the one people forget
Double layer of RF shielding cloth
Snap closure is quick to do properly
Very widely reviewed on Amazon

Cons

No published lab testing - run the walk-up test the day it arrives
Compact; large or multi-button fobs can be a tight fit
PU exterior is less durable than ballistic nylon

Check price on Amazon

Best for large fobs

2. DefenderShield Ultra Armor Key Fob Faraday Bag

$39.99 as of Oct 12, 2026 09:00 UTC

The reason to pay more here is room: a 5.5 x 3 x 0.2 in interior swallows a large proximity fob or a fob on a loaded keyring that won't seat properly in a compact pouch. The exterior is water-resistant military-grade ballistic nylon and the closure is a VELCRO strip rather than a fold-and-tuck flap, which is faster one-handed and harder to get subtly wrong. DefenderShield states its Ultra Armor shielding blocks 0-90 GHz. It's a single bag costing more than a two-pack of budget pouches, so it's the premium pick rather than the value one - and if you need to cover a spare fob as well, you're buying two of them.

Pros

Roomiest interior here at 5.5 x 3 x 0.2 in - fits large fobs and loaded keyrings
VELCRO closure is quicker one-handed than a fold-and-tuck flap
Water-resistant military-grade ballistic nylon exterior
Manufacturer publishes a shielding range (0-90 GHz)

Cons

One bag for more than a budget two-pack
Doesn't cover a spare fob unless you buy a second
Sold out on DefenderShield's own store when we checked - Amazon was the in-stock channel
Some retailer listings wrongly describe the closure as magnetic; it's VELCRO

Check price on Amazon

Our pick: Lanpard Faraday Bag for Key Fob (2-Pack)

Buy the Lanpard two-pack. It covers both your daily fob and the spare in the drawer for less than a single premium bag, and a cheap bag you've actually tested does the job. Step up to the DefenderShield Ultra Armor bag if your fob is too big for a compact pouch or you want a manufacturer-stated shielding range. Whichever you buy, run the walk-up-to-your-car test the day it arrives, and again every few months.

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Frequently asked questions

Does a faraday bag actually stop keyless car theft?: It stops the relay attack specifically - the one where thieves capture your fob's signal near the house and repeat it to the car. Sealed in a working faraday bag, the fob can't respond to the car's query, so there's nothing for the relay to forward. It does nothing against theft methods that don't involve your key signal, like a broken window or a flatbed tow, so treat it as one cheap fix for one common attack rather than complete protection.
Will a faraday bag damage my key fob or drain the battery?: No. The bag blocks radio signals in and out; it doesn't put any load on the fob. If anything a fob that isn't constantly waking to answer your car may see slightly less battery drain. There's nothing magnetic in these pouches that would harm the electronics.
Can I just use aluminium foil, a metal tin, or the microwave instead?: These are the classic improvised versions and they can reduce the signal, but none of them is reliable. Foil tears and stops sealing, a tin usually has a seam or a lid gap that leaks, and a microwave is designed to contain one specific frequency, not the range a fob and its relay use. They also all fail silently - you won't know it stopped working. If you try one anyway, run the same walk-up-to-your-car test, and re-run it often.
My car has a motion-sensing fob that goes to sleep. Do I still need a bag?: Some manufacturers now ship fobs that stop transmitting once they've been still for a while, which does close the overnight relay window. Ford's motion-sensing key fob is the clearest published example: Ford says it sleeps after 40 seconds without movement and won't respond to a relay attempt until it's picked up again. Two caveats. It only helps once the fob has actually been sitting still that long - a fob in a coat pocket by the door that gets knocked as people pass may keep waking. And it does nothing for a spare fob that's an older model without the feature. Check your owner's manual for whether yours has it; a bag is a few dollars and covers the case where it doesn't.
How do I know my faraday bag still works?: Test it, and keep testing it. Seal the fob, walk to the car, and try the handle and then the ignition. If either responds, the bag isn't sealing. Do this the day it arrives, with each fob separately, and again every few months - the conductive fabric wears with repeated folding, and a bag used daily for a year is not in the condition it shipped in.

Sources

Specs and prices are compiled from the sources above and current as of the update date. Availability and pricing change — confirm on the retailer page before buying.