Selena Gomez -- Cops Rush to Calabasas Home ... Again

Selena Gomez may want to rethink living in a free-standing house ... because she sounded a 911 alarm yet another time Sunday ... this time because she feared a burglar lurked inside her home.

Selena has cause for concern -- a stalker has broken into her property before, got arrested, got out and made a beeline for her home. He got arrested again and thrown in jail, but he was out in a matter of days. He was admitted to a mental health facility as of June 20, but is only required to be there for 30 days.

Selena got home Sunday night just before midnight and saw the back door flung open.

Cops rushed over but found no one inside and no evidence of forced entry. It's possible she left it open herself, but Selena is freaked out.