Have eyes in the back of your head
Definition 1 of 1
Pro Tip 1/3Vigilance Required
Use this phrase when someone needs to be extremely careful or aware of their surroundings. 
With toddlers running around, you really need to have eyes in the back of your head.
Pro Tip 2/3Metaphorical Sense
Remember, it's a figure of speech. No one actually has extra eyes; it means being alert and perceptive. 
He must have eyes in the back of his head; he noticed the door opening, even from his desk facing away.
Pro Tip 3/3Not Literally Possible
Don't confuse learners; emphasize the expression is used humorously or jokingly, not to describe a physical ability. 
My mom seems to have eyes in the back of her head, she always knows when I'm up to something.