Actually, they x-ray them.

[soon it's their turn...Jackie takes off her shoes and piles her purse and shoes into a small bin that goes on the conveyer belt, her suitcase following behind]

[she steps through the metal detector...and sets it off, having to stand still as they figure out it was her keys in her pocket that did it...after that, she's cleared to go]

[she looks back to make sure Sherlock is getting through alright while she's trying to get her shoes back on]