Smoke smell in apt

I'm trying to move into the area, and the old buildings have many tricks up their sleeve. The most worrysome is a cigarette-smoke-like smell that appears in the apt frequently. Our son has asthma, so anything like that is not good. The fact that it happens several times in the deep of night makes me think it's not the neighbors smoking. Perhaps the heating system? Has anyone had a similar experience and figured out what's going on?

Cheers

You know, I've had this on occasion in my current apt and in my previous place. I'm not sure what it is, but I also have asthma; it usually flares up when I'm around cigarette smoke, but the smell alone hasn't caused it to happen. Not sure if that's helpful at all...

the same thing happens in our office when someone smokes in the stairwell..

Air currents are tricky, someone is probably smoking in your building somewhere. Good luck. I've been bedeviled by this scenario many times.