monitor (to regularly check or watch over a period of time in order to find out what is happening): The nurse will monitor his heart rate.
observe formal (to watch someone or something carefully and attentively): The police were observing his movements.
watch (to look at attentively over a period of time): I want to buy a ticket, so please watch my bags for me.
keep an eye on informal (to watch or look after): Jane will keep an eye on the children till I get back.
keep track of (keep fully aware of, remain informed about): It’s my job to keep track of everything here.
keep tabs on (to watch carefully): You must keep tabs on your children.
