[PorKIA Pig]

Having watched the segment on the One Show, I think the obvious thing is to do is keep the key fobs in a 'faraday cage' pouch/box and/or add some sort of secondary protection to the vehicle (modern day versions of the 'Krooklock', disklock etc).

Not that you should have to with a modern vehicle, but I suppose we are where we are.

I wonder if ultimately Kia can find a way to deactivate the keyless software on the vehicle, and owners can go back to pressing the button on the fob.

As you rightly point out, 'Keyless' is a 'solution' to the really insignificant, minor matter of pressing a button on a key fob!

Having read all the reviews and comparisons I could find, I decided to buy Defender Mini Signal Blocker pouches, these seemed to come out on top every time, but turned out to be a real disappointment. I ordered them direct from the makers, Solon Security.
On arrival they looked to be well made and accomadated my Kia Niro 4 smart key very well. To begin with I assumed they were doing their job, this was a mistake. On the second day of using it, when standing next to the car with the key still carefully tucked up in the velcro fastened pocket, the car door mirrors unfolded, indicating that the key had been detected! I was surprised, disappointed and annoyed. I then experimented with the orientation of the wallet and it seemed to be "leaky" depending on how it was held. If just loose in the hand the key would be detected. If the closure was given some extra help by grasping it, the key was undetected. This is not satisfactory and very hit and miss. There was absolutely nothing visibly wrong with it. It looked well made and had only been used for a day. To cap it all the other wallet behaved in exactly the same way. I dare say that they reduce the RF signal strength but in my experience do not block it. As I do not know how sensitive the detection equipment is that potential car thieves use, I want something that blocks the signal completely. They should be renamed Signal Reducing Pouches.
I will say that when contacting the company, Solon Security offered me a refund straight away.
I am now in the process of making my own small boxes from aluminium.

 

[PorKIA Pig]

Having proved that two brand new, supposedly quality, signal blocking pouches don't work, I am now very sceptical of any of the "fabric" type. It seems to me that the UHF 433Mhz signal in question will find it's way through the smallest of gaps as I found out on the Defender pouches I tried. I have subsequenty also tested biscuit, toffee and shoe polish tins all with
negative results and all of course ferrous metal, tinplate.
I am now convinced the only viable solution other than the disabling of the feature is the use of the type of aluminium box mentioned by Daveyboy123
these being CNC machined from solid aluminium.
To this end I have tried to emulate them by hand. However I have not found it easy and not yet achieved the complete signal blocking required. My accuracy wth needle filing is not yet good enough. One of the boxes is shown here:-

I guess at some point I will bite the bullet and lash out the money for professional ones.
Given the rise of relay theft over the last couple of years. I think it is scandalous that Kia can't write some lines of code to give the option in the car settings to disable/enable smart keyless entry.