Yeah I've done that^
Easily done. Went to the car, unlocked it using the fob, didn't open any doors. Popped the boot also with fob, put the keys down in the boot with my stuff by mistake. Shut the boot and got distracted by something in my garden. Few seconds later I hear the clunk of the car locking itself! Lol!
Luckily I have a spare and you really should get a spare too :)