Oh hey, I like this variant! So... both the BLE beacon and the phone have a faraday cage, and if they ever appear together outside their cages, the phone wipes?

Perhaps less likely to go wrong than my original proposal when living normal life, as it might wipe if the BLE signal randomly gets lost.

It would be nicer if you could leave phone in cage during security, and remove beacon while loading airport trays ("remove all electronics from their cases..."). the only chance for a failure mode is only when you're going through security, and have the fob outside its case..

But you'd need to be able to leave your phone in the faraday cage pouch while going thru security, which is only ok if they don't notice... (maybe they commonly don't notice small faraday pouches aren't empty... Maybe they wouldn't if you had a secondary mobile device...)