I'd also be very frustrated. If I were in your situation and had suffered through several such annoying experiences, I'd try to be as pro-active as possible, e.g. keeping the device in some kind of locked container so that you'll be able to make your request before anybody starts pawing, er, inspecting it.

As essxjay has just posted, it would probably be best to allow some extra time for yourself at the checkpoint.

I hope somebody here can come up with further practical advice for you.

Cheers,
Fredd