This came up on another thread but I know several of you travel here so I thought I would give the details as they are being obeyed quite strictly.
No smoking inside any buildings open to the public except in ventilated designated rooms. The rules on ventilation are quite strict so these rooms are extremely rare.
No smoking outside in public areas, so in the grounds of hotels, other buildings, street, car parks etc. except in designated smoking areas.
No smoking in cars with kids.
Fines are imposed on both the smoker and the establishment.
If I remember correctly the fines for the smoker are:
First offence: HKD 50 (about an average days wage)
Second: HKD 160
Third: HKD 480
Fourth: HKD 1400 and potentially prison.
The enforcers, at least around here, are local government employees who are not in uniform so don't think if you can't see a cop you are safe.
I am seriously surprised how effective it has been.