Smoke can go through closed vents and other tiny spaces.
Even when a vent is closed there are still some tiny gaps that allow some air and smoke to pass through.
Smoke can also seep through and go through gaps around air conditioners, door gaps, and even through some filters.
If you're smoking Cigarettes and trying to keep the smoke from leaving the room there's not much you can do other than opening the window in the room you're smoking in.
No matter what you do, if you smoke indoors, the harmful chemicals from your second-hand smoke will hang around for hours doing real harm to your kids and increasing their risk of illness.
Secondhand smoke can still spread through your home.
The smoke can travel through doorways, cracks in walls, electrical lines, ventilation systems, and plumbing.
Smoking can also leave residue on walls, curtains, etc and can and will leave a smell in the room.