Jamieson, Fausset and Brown on 1 Samuel 19:11-12

11-12. Saul sent messengers unto David's house, to watch him, and to slay him--The fear of causing a commotion in the town, or favoring his escape in the darkness, seemed to have influenced the king in ordering them to patrol till the morning. This infatuation was overruled by Providence to favor David's escape; for his wife, secretly apprised by Jonathan, who was aware of the design, or by spying persons in court livery watching the gate, let him down through a window (see on Jos 2:15).