[MystroX5]

For those of you that store your BMW in the garage with your key fob within range of it parked: Storing your key fobs in a metal can acts as a faraday cage and will greatly improve your fob’s battery life as it cuts off constant contact with your vehicle and any “comfort/proximity” features you might have activated.
I found this to be true with Porsche fobs as well.

[mobilejo]

In the UK at least, BMW keys now go to sleep after a short time if no movement of the key is detected. This is to prevent keyless relay theft, but does also mean that if the key is not moving, its not broadcasting a signal so has the same effect as a faraday device for saving battery.

Having said that, I still put my key in a faraday pouch as a backup measure. Keyless theft is common over here.

[eelnoraa]

Faraday cage requires the case to be connected to a constant potential, typically ground. If left floating, it really does nothing, revisit maxwells equation #1.

[MystroX5]

Originally Posted by eelnoraa

Faraday cage requires the case to be connected to a constant potential, typically ground. If left floating, it really does nothing, revisit maxwells equation #1.

It blocks any and all signals to and from fob. Example: Wrap your cell phone in a single layer of aluminum foil and see if you can call or get any signal to or from it.

[TurtleBoy]

Originally Posted by mobilejo

In the UK at least, BMW keys now go to sleep after a short time if no movement of the key is detected. This is to prevent keyless relay theft, but does also mean that if the key is not moving, its not broadcasting a signal so has the same effect as a faraday device for saving battery.

Having said that, I still put my key in a faraday pouch as a backup measure. Keyless theft is common over here.

Same way in the US, I think the time period is a minute of not being moved.

[mobilejo]

Originally Posted by eelnoraa

Faraday cage requires the case to be connected to a constant potential, typically ground. If left floating, it really does nothing, revisit maxwells equation #1.

These pouches do work to block the signal - I've tested a few myself.

https://www.autoexpress.co.uk/produc...-blockers-2023

[tooloud10]

This is a somewhat legitimate concern on my '99 Porsche or '08 M3, but not on a modern car like the G05.

[Marty in NY]

Originally Posted by eelnoraa

Faraday cage requires the case to be connected to a constant potential, typically ground. If left floating, it really does nothing, revisit maxwells equation #1.

Yes, a true faraday cage would be grounded but in this case we are only attempting to block a two way signal and they work fine. My wife and I use them because for some reason whenever we are both together and we both have our key fobs with us, the car connects to hers instead of mine and I am usually the driver. This means all the settings she set up are initiated and they don't work for me. Putting her key fob in the faraday pouch has completely solved the issue, the car does not recognize her key when it's in the pouch. When we first got them, we tested them by putting both our keys in the pouch and walking up to the car, which was locked. My key was in my pocket, her's in her purse. The car would not respond to either of us as we tried unlocking the door via the handle as it always used to. We also unlocked the car and then put the key in the pouch and the car would not start until I took mine out of its pouch.