I hated it when my parents snooped when I was a teen, but now as a mother of teens myself, I can totally understand why they were doing it!

Also with my son (16 this December) there is a lot of peer pressure at the moment. At least he can say "No way - I'm not doing XYZ - my Mum ALWAYS finds out" (As sirrahbed says - I have an uncanny way of knowing when he is up to something he should not be doing, and he ALWAYS gets caught out!!!)