The Bible records: And the LORD God formed man of the dust of the ground,
and breathed into his nostrils the breath of life;
and man became a living soul.
(Genesis 2:7) According to Jewish law life ends (and death begins) when a person stops breathing. The typical test is to put a soft feather near the nostrils and observe if it flutters. Brain death has no validity in Judaism; a person is alive until they stop breathing.