Most airlines will cut the locks off your luggage.
None <><><> Depends on the age of the child. MOST airlines have a procedure called "Unaccompanied minor". There are limitations on which flights this can be used. Check the websites or call the airlines you are considering.
Authentication alone is not secured. That should happen on secure channel otherwise man in middle attack is possible.
Yes. With most airlines you indeed can.
i dont know where you are from but i know you can travel alone with SAS from 13 years old
Yes
Most airlines let you fly alone at about 13/14.
More than 150. There are quite a few in the USA alone. See the related link about flightmemories. Some contributors have flown in well over 100 airlines.
you have to be 16 years old to travel alone with Monarch most other airlines are 12 or 14 years.
a knife/ flashlight/ gun/ water if driving/ extra batteries for everything/ protein bars/
They can be left alone in a secure place, in a room, run or hutch, but don't leave them in the open where cats could get them and they could escape.
Most airlines have very specific policies concerning children flying alone. It's allowed at a certain age by some, it's completely not allowed at all by others, and by some there are conditions for your child flying alone. The best way to find out is to contact the airline in question, or find out on the airlines official site.
I don't think any metro stations in Madrid do.. I had to carry 4 months of luggage on the Metro.. Lets just ssay i didnt make it alone, and ended up getting help from some toothless guy..