Or keep it in a faraday bag and have the phone wipe if it sees it. If you're ever searched (or otherwise indisposed), they'll open the bag and wipe your phone for you.
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...)
Only once you're getting invasively searched would they (ideally) dump the pouch out into the tray with your phone.
Isn't that the same issue here that resulted in felony charges? Border agent was given a duress PIN and wiped the phone for the owner. Now owner is charged.
This requires no action whatsoever from the phone's owner, you could even be unconscious/dead and it would still work.
I think this sums it up for me:
- wipe-on-lost-signal = easier to claim as legitimate anti-theft mechanism. Harder to claim you forgot about it (because you'd have the actively live a life where they don't lose signal)
- wipe-on-found-signal = easier to claim as accident. ("I forgot that little faraday keychain was in my bag, and haven't touched it in years since I was on company project X"). Harder to claim it's a general anti-theft mechanism, as it requires a threat model of someone laying all your stuff out together on a table.
EDIT: Maybe it's in a little pouch attached to the phone itself, and they think it's a find-my-object tracker to inspect, but it's actually a beacon that wipes on detection. But yes, this is getting a little ridiculous in terms of plausible deniability :)
Both approaches have situations they wouldn't work in. If you're extra paranoid you could do both.