peek at (someone or something)
To get a quick, cursory, often sneaky or surreptitious look at someone or something. I peeked at the boss's computer and saw an email about a possible round of layoffs coming up. Campus guards caught him trying to peek at the women getting changed in their locker rooms.
peek at someone or something
to sneak a glimpse at someone or something. Now, don't peek at me while I am changing my shirt. I peeked at the dessert you made. It looks delicious.