Albert Barnes Commentary 1 Samuel 19:11

"And Saul sent messengers unto David`s house, to watch him, and to slay him in the morning: and Michal, David`s wife, told him, saying, If thou save not thy life to-night, to-morrow thou wilt be slain." — 1 Samuel 19:11 (ASV)

Saul’s plan was to surround the house at night and to have David killed as soon as he came out unsuspectingly in the morning.