Faraday bags a con?

Many fobs have several keys in them:

1. an active one, where you press the button to eg unlock the doors or open the boot
2. a passive one, which the car can query to see if it's in range. If so it'll unlock the doors / start the engine. Could be powered inductively or battery powered in the fob
3. a mechanical one, for getting into the car if the battery is flat

'Keyless entry' can be some variety of no.2. The button is no.1. The difference is that in no.1 the fob sends out a signal when activated, while in no.2 the car is sending out requests all the time and listening for the fob to answer.

The usual problem is that your key is sitting on the hall table, but the miscreant can record the car's challenge standing next to it, walk up to your front door and replay the challenge. The fob answers and the miscreant records the response. Then they replay the response next to the car and the doors open.

If you put the fob in the shielded bag then (in theory) the fob doesn't hear the challenge and so never replies. That means they can't nick the car while you are asleep.

When you take the fob out of the bag you're likely standing near to the car and it doesn't matter if the miscreant unlocks the car because you were unlocking it anyway. If they're going to steal the car at that point they'll need to physically overpower you, which they could have done without any key fob spoofing. But that's a whole different crime from sneaking away with the car at 3am.

Theo

Thanks, Theo.

It would help if I kept my keys in a biscuit tin when at home?

That would probably do the job. Most of the fobs use 433 or 868MHz (315MHz for some imports) so if you have a good shield against that signal then it should work (obviously the lid needs to be on!).

Theo

I bought some metalised plastic pouches, two of which I have in my wallet, with the chip-n-pin cards between them. Couple of quid off Amazon.

We have a metal bread bin I've started using (see post about scrotemobiles).

At the end of the day you can only do so much. If these people want your car, they are getting it. And if that means dragging you (or a loved one) out of bed with a knife to your throat then that is what they will do.

I keep my contactless entry fob in a small foil-lined wallet (from the big river). Partly to prevent man-in-the-middle attacks by thieves but also to stop the car noisily unlocking and re-locking every time I walk past it with the key on me when I'm not wanting to use it.

I'm on my second one because the first one didn't really work, it mostly stopped the car seeing the key but sometimes it still did see it. So I deduce that some of them only just reduce the signal enough, and maybe that may not be enough to stop high-power repeaters from seeing them?

nib

I've got wire mesh in my walls and on my roof and foil backed plasterboard Probably good enough

None of those nasty glass windows, I hope? :)

It's not the foil. Tiny thicknesses of foil are sufficient. But, the construction of the bag matters - whether the opening is properly covered, for example. It probably also helps if there's electrical continuity between the front and the back.

Won't work, Turnip. Nowhere near RF-tight. An old fashioned biscuit tin is pretty good for keeping radio frequency emissions out. If anyone's inspected an RF-tight container, they will be aware that there are *no* gaps in the casing and all joins are overlapped. Unless you're living in some sort of hovel with no doors or windows - or else they're all shuttered up with grounded metal - RF will leak in like a sieve.

We don't want a resonant cavity either.

When you use the buttons on the fob, it locks or unlocks the car as required and then changes the code, so no-one can copy and re-use it - called a "rolling code".

When you use the button on the door handle, the car sends a signal to the fob and the fob replies, opening the car. This is where there is a vulnerability. If your fob is in the house someone can stand near the car with a transeiver, while an accomplice stands near the house with another one. When the first person presses the button on the car, the car sends a signal, but the fob is too far away. However, the first transeiver picks up the signal, passes it to the second and that sends it to the nearby fob. The fob replies, but again is too far from the car. The second transeiver picks up the signal, passes it to the first and the first sends it to the car, which unlocks and can be started - known as a "relay attack".

The Faraday pouch stops the fob from responding to the car's signal, whether directly or relayed and so prevents a relay attack when your car is locked up and your keys are in the house.

Which they may do for a high-end car, but are less likely to do for a typical family car.

Apparently the microwave is a good place to keep certain types of key . . . remember to take them out when cooking :-)

On many BMWs you have to touch the door handle to trigger the unlock. (Touch handle, car sends signal, fob responds, doors unlock.) You can disable it by removing the cable from the handles. Then it doesn't detect the touch and query the fob. You unlock it by pressing the fob button. By far the most sensible way to unlock a car... unlock when I physically demand it.

Out of interest, I've often seen people continue mobile phone conversations in a lift. I've always assumed that lifts are pretty much metal boxes (which are earthed via the cable supporting them and metal guides on the sides). Why do they seem to make such poor Faraday cages where mobile signals are concerned?

Oh yes.

A few years ago a friends boss had some high end Mercedes or BMW. Either way the last he saw of it was when he was woken by the puff of air brakes as the grab loader the scrotes had driven to his house lifted it off the drive and over the rising bollards.

Lifts are not made to be RF-tight. They have gaps, even if you can't see them. It only takes a slight opening to let RF through. That's why the old-fashioned biscuit tins (you don't see them so much these days, if at all) are so effective. They weren't made to be RF-tight, but they *were* made to be air-tight, and in an all metal enclosure, that's the effectively the same thing.

No. small leaded lights. NICE windows