Am I being paranoid but I am told I need to keep the keys of my 2018 XJ in a metal box all the times to prevent it being scanned. This includes not only when I am at home but at any time.

Also advised to use a steering lock.

 

I would definitely advise using a Faraday pouch to store your keys in (both keys so you'll need two pouches)

Also a physical deterrent such as a Krooklock is ideal to deter would be thieves as it is something else for them to get past