?The keys can't be hacked like in the old days as they are unique to the car and the module in the car.
Replacement keys also need a new module in the car so it can be expensive.
The pouches just block the signal that the key sends to the car all the time to enable keyless entry.
The signal from the key only works at a short distance so the theft method is to hold a device near to the keys (by your front door normally) which then boosts this signal enabling the car to be opened and then started and driven as it's being fooled into thinking the key is within range.
No keyless entry then no pouches needed.
The devices they use are pretty short range too so I wouldn't worry about someone following you around Tescos waving a carrier bag by your ear.