I do roadside assistance and one of those tasks is unlocking vehicles.
Often owners have locked their keys in the trunk and modern cars, with electronic trunk releases the vehicle security system disables the trunk when it detects a break-in.  There often is no way to enter the trunk from the cabin as there is no way to release the seats from within the passenger compartment.
So the owner is no closer to getting their keys than they were before I opened the doors.
With some cars I can remove the lock from the door to 'unlock' it using tools.  For many cars this cannot be done.

I have seen a mobile locksmith use a diagnostic tool to clear the vehicle's security and release the trunk.  They left before I could inquire about the tool.  I've inquired with a few tool sellers on amazon if their device could unlock trunks or clear security and they're mum about it (probably due to thoughts of thieves using their tool).

Could you recommend a diagnostic tool that is capable of doing this (or, at least, disable the security so the car's own trunk release will function) that isn't terribly expensive or bulky, since I would really only have one use for it (don't want people to know I've got it or they'll be asking me to do garage level diagnostics on the roadside).  And I certainly don't want one that re-codes keys/fobs - unless I can get paid what the actual locksmiths get!!

That ODBII bluetooth one, if it can be used to clear security lockouts, would be ideal... ?