"Keep an eye out" is a common expression used to ask or remind someone to remain vigilant or to be watchful for something in particular. There are several synonyms that can be used instead of this phrase that can add variety to your writing while maintaining the same meaning. Some of the synonyms for "keep an eye out" include "keep watch," "stay alert," "be mindful," "be observant," "remain vigilant," "be on the lookout," and "keep a lookout." Using these variations can help spice up your writing and avoid repetition while conveying the same message to your audience.