The point of being a teenager is having the opportunity to sneak around behind your parent’s back.
I grew up in the 60’s and 70’s and so been there, done that. My parents were clueless about drugs. I would bust my grandson all the time. Come home late and hit the refrig “Oh I see we have the munchies...”, or “You are a little too bit chipper and talkative for 2am...”, or “What’s up with the camel routine?”.
All tell tale signs of doing something. Of course you have to have multiple indicators...