Hogwarts is hidden to Muggles. As a potential threat of being found by muggles, the founders and other professors charmed hogwarts to have protection from wondering outsiders, showing the appearance of half destroyed ruin village covered in tape along with warning signs. If a Muggle looks at it, even today, they see an old ruin with a sign saying: "DANGER, DO NOT ENTER, UNSAFE".

Also due to the magic being performed at hogwarts, Muggle technology cannot be used within the grounds of Hogwarts and the trace is lifted while the students are within school grounds.