see something out of the corner of your eye
From Longman Dictionary of Contemporary Englishsee something out of the corner of your eyesee something out of the corner of your eyeNOTICEto notice something accidentally, without turning your head towards it or looking for it Out of the corner of her eye she saw the dog running towards her. → cornerExamples from the Corpussee something out of the corner of your eye• Out of the corner of her eye, she saw a man running out of the store.