keep a weather eye on something/someone
keep a weather eye on something/someonemainly BRITISH
If you keep a weather eye on something or someone, you watch them carefully so that you are ready to take action if there are problems. Keep a weather eye on your symptoms and stay alert to any changes which occur. Amy moved away from a neighbourhood where she'd kept a weather eye on an old lady. Note: Other prepositions are sometimes used instead of on, for example out and for. The police were there, keeping a weather eye out for trouble of any sort. Note: This expression was originally used by sailors, who had to keep a constant watch on the weather and wind direction.