Thanks caryh,
I've just removed my first one, after 14 days it expires and had a good look at it. I can't even see a battery so it must be very small. Other than the very thin needle I see no other metal.
Flight to LHR this afternoon, not expecting any problem, but will take my glucose finger sticks - just in case.
Edited to add: I'm not certain it has a battery. It's a passive NFC device which don't need power sources (like your NFC credit card). The packaging doesn't mention any special disposal requirements, which it would have to do if a battery was present.
Last edited by ExXB; 7th Sep 2016 at 06:32.