look·out 
/ˈlʊkˌaʊt/ noun
plural look·outs /ˈlʊkˌaʊt/ noun [count] 1 : a person who watches an area and warns others if there is danger
▪ The troops posted a lookout for the night. 2 : a high place or structure from which you can see a wide area
▪ The mountain road had several lookouts where you could enjoy the view. ▪ a lookout tower
▪ The troops posted a lookout for the night.
▪ The mountain road had several lookouts where you could enjoy the view. ▪ a lookout tower
be someone's lookout
Brit, informal — used to say that someone who makes a bad decision or does something foolish is responsible for the result and will have to deal with it alone ▪ If he wants to spend all his money on expensive clothes, that's his lookout.
keep a lookout for
: to watch for (something or someone)
▪ The police officer walked through the neighborhood, keeping a (sharp) lookout for any suspicious activity.
▪ The police officer walked through the neighborhood, keeping a (sharp) lookout for any suspicious activity.
on the lookout for
: looking or searching for (something or someone)
▪ An avid shopper, she was always on the lookout for sales. ▪ The police are on the lookout for two men who escaped from custody yesterday.
▪ An avid shopper, she was always on the lookout for sales. ▪ The police are on the lookout for two men who escaped from custody yesterday.
