Help needed regarding relay theft

[BigSpoon]

Hi all,

I've been reading about relay theft and I understand that if the keyfob is in the house somebody outside could amplify the signal of the keyfob and gain entry and also drive the car away. I've also read that by keeping the keyfob in a Faraday pouch/box it would prevent this from happening.

My question is if I drove to say tesco and there was somebody near my car with the tech stuff needed, would they be able to grab my signal before I got out of the car, locked it and put it into a Faraday pouch and then use it once I'm in tesco or can they only do it in the moment??

Thanks