All I'm concerned with on this subject is the very real exposure of high-tech car thieves. Those using illicit programs on mobile devices that can home in on the signal your modern car emits. Over a matter of hours such programming can basically decrypt the signal and the alarm system when a car is parked so they can steal it. The reason why I always place my fob in an unused microwave oven, which blocks those signals in all directions.
Something I learned about even before I bought my car, having paid no real attention to how the market and technology had changed in the last 17 years. When up to that point, I thought just having a quality passive alarm system used to be enough. I had no idea that current keyless-entry had become so problematic!
Of course paralleling this exposure is the aggressiveness
of some auto manufacturers to continually improve the encryption of these signals to limit such thefts. Something that most of them now are reticent to discuss publicly for the obvious reasons. And if you own a Hyundai or Kia, your car is likely to be woefully behind the curve of such anti-theft technology. Now touted as some of the easiest cars to steal, effectively bumping Honda off that unwanted pedestal.
But the fragility of faraday bags for an electronic keyfob always seemed to haunt me, so eventually I stopped bothering with them altogether. Luckily I seldom park my car anywhere else for hours on end, so hopefully that is enough apart from having a manual transmission that most people can't even drive here.
Do these bags "work"? Yes, provided there are no tears or breaks in the metallic material, especially in consideration of all the seams that keep it together. Otherwise they quickly become useless, where even a pinhole sized opening is enough to render a faraday bag useless. Between constantly withdrawing my keyfob from the bag and my pocket, the inevitable holes and tears happen.
But then like everything else made these days, they aren't made to last. Whatever it takes to establish a "repeat customer". I gave up on my third bag some years ago. Pity, as I'm convinced if they really wanted to design a bag that would last they could.
