What are you trying to do exactly? I alternate my two master keys every month so both batteries die at roughly the same time and can be replaced at the same time. I don't keep the one that's not on my key chain in a faraday bag. I just put it in a drawer.

 

How will a faraday bag stop working? Please clarify what you are asking. Faradays bags will work forever, as far as i know.

 

Depends on the bag. Some of them are simply a light metal coating on one side of the plastic, and that can and will scratch and wear off. Some are more robust and use an actual metal mesh between multiple layers of plastic and can take a lot of abuse.

Personally, I never use one.. and I also never use the buttons on my FOB either (to avoid a long range sniffing of my FOB in a public location). I lock and unlock my CRV with the button and handle on the drivers side, which only initiates a short range (less than 10 feet) handshake between FOB and vehicle. FOB batteries also last a lot longer too with my approach. Over 5 years now on my CRV, and my FOB is still in good working condition on only the second battery it has ever seen.

 

Test it. When I put my fob in the faraday bag and go up to the car, it does not unlock. When I take it out of the bag the car unlocks when I get up to it.

 

+1 to the above post.
I have two of them for my two key fobs.
The one which I use regularly, has become weak over time and I'm able to open the car even without taking the fob out of the pouch (the whole thing need to be really close to the sensors though). Even the start/stop button work sometimes, with the key fob inside the faraday pouch.

In your case, if you are not regularly using it, any faraday pouch should do just fine. Like others said, buy a good quality one and test it out.

 

I was hoping to be able to bring the second key fob on long driving trips as a spare in case I lost the first one. Normally, I keep it at home. I don't use it for locking/unlocking doors; I use the buttons on the doors.

 

I'm just gonna come out and say it... A Faraday bag is pretty useless. Thieves are using your VIN and an OBD device to steal these vehicles, not some sort of relay attack. An old fashioned steering wheel club would be a better device to use as a theft deterrent.

 

Actually I wasn't thinking about theft. I was on a long, few days, trip with my partner. I put the second key fob in the glove box in case my original got stolen. My key fob was in my pocket as usual since I don't use it to lock or unlock the doors, I use the door buttons instead. I stopped for gas and went into the store while the pump was going. While I was in the store, my partner tried to open the door to get out and use the bathroom but the car alarm went off. I realized it was the fob in the glove box that activated it. So, I wanted to know if a faraday bag would have prevented the fireworks.

 

I put the second key fob in the glove box in case my original got stolen.

Issue here is that if your key fob is stolen, then most likely your car (with the second key in the glove box) will be gone as well.
If it's only lost, then you will not be able to take out the second key, which is inside a locked vehicle. Better to leave the second one with your partner.

While I was in the store, my partner tried to open the door to get out and use the bathroom but the car alarm went off

The car will auto lock (even if there is no second key inside) after some time of inactivity after shutting off the ignition. And the people inside will be able to open even if it's locked. Safety feature.

I wanted to know if a faraday bag would have prevented the fireworks.

Not really. Faraday bag prevents the car from detecting the fob. If the person need to come out of the locked vehicle without triggering the alarm, take the second fob out of the pouch and unlock using the second fob.

 

Signal extender car thefts are really common, faraday cages prevent this.

 

It's pretty much nonexistent in N America.

 

I would guess that a Faraday box -- one that is rigid -- is likely to stay effective for a much longer time than bags/pouches that bend and fold?