Billie Eilish's family home was burglarized in L.A. Thursday night ... and police arrested a suspect thanks to a quick-thinking house sitter as the crime was in progress.
Law enforcement sources tell TMZ … cops responded to the house in Highland Park around 9:15 PM after receiving a report of someone scaling a fence to gain access to the property.
The masked intruder was apparently wearing all black and lurking around the backyard. We're told the house sitter -- who was not present at the location -- received an alert on an electronic device showing the unidentified man on camera. The employee didn't recognize the person and quickly called police.
Cops responded to the scene and nabbed the suspect about one block away during a sweep of the area. Investigators tell us they don't believe anything was stolen from the house, which they confirm is owned by Billie's family.