How to Tell if Someone is Vaping in Your House: Hidden Signs How to Tell if Someone is Vaping in Your House: Hidden Signs What does the smell of stale tobacco smoke mean? Thirdhand Smoke Resource Center In secondhand vape, scientists smell risk American Heart Association The safest vape is the one you never start. Flavoured vapes were designed to feel harmless: Candy taste. Fruit smell. Cool packaging. Viral aesthetics. But your lungs don't care about the flavour.