Is it true doctors wont know teens smoke if they listen to their lungs using a stethescope?

Yes: Being a smoker doesn't necessarily mean that a doctor can pick it by listening the patient's lungs. Smoking doesn't cause any special audible phenomena, rather than auditory abnormalities that are common in other types of pulmonary/cardiac diseases - bronchitis, asthma, copd, congestive heart failure. However, by listening to a smoker's lungs, the physician may be able to smell the smell of smoke.

Yes,but.....: They don't hear it in your lungs, but you may be giving off enough smoker stank that they would suspect so anyway.Unless you just light up occasionally smoking destroys some of the sensitivity in your nose and won't be aware of the lingering smokers odor your hair and body give off that others can smell.