This is going to sound weird and implausable but I do occasionally smell cigarette smoke in my home. Neither DH or I smoke, nor do my neighbours either side of me or any visitors to my home. My Father smoked and I feel its him trying to contact me. He died well over 20 years ago and he was a lousy father, husband and person. Whenever I smell the smoke, its usually only 2 or 3 times a year, I just tell him to F... off, I dont know what you want but its too late or something like that, and the smell goes. Yeah I know it sounds crazy but its true.