Could someone know when a human being open their front door? I went over to my friend's house yesterday and today and today...

I went over to my friend's house yesterday and today and today her dad come home and said that she opened the door two times respectively day and wondered who be over at the house. How could he know this?
Buying gas?
Answers:    As a Dad myself, I can't divulge this method !!

It's something us parents keep a closely guarded underground!

Sorry!

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Is your closet(s) tidy?
Ooooh creepy! He's watching you! Or he set something up like a stick at the door which you didn't distinguish so that if it moved he could tell. She be home alone right?