The abandoned house was not quite as abandoned as it first appeared. There were smudges on the door, barely visible because the repeated attempts to clean the door of said smudges.
But Sherlock noticed.
The yard was carelessly untrimmed, but at regular intervals there were occasional footfalls which had not been covered up.
And Sherlock noticed.
And the security system, almost small and unnoticeable, was on high alert, letting the jewel thief ring know that they had visitors.