keep one's eyes peeled
US, 19th century. Peeled probably refers to keeping one's eyelids retracted.
- (intransitive, idiomatic, (with "for")) To be on the alert, to be watchful.
2003 November 14, Laura Bly, “Sailing into the past”, in USA Today:
- lookouts posted to the port and starboard bows keep their eyes peeled for the ghostly outline of approaching traffic.