Good Afternoon.
FTR: I make my living as a Fire Alarm Technician
The different types of fire detectors being discussed so far: Ionization smoke detectors, Photoelectric smoke detectors, and Heat detectors.
The short answer to the OP is that cigarette smoke is not very dense. It has been filtered through your lungs. Neither type of smoke detector is very good at picking up cigarette smoke unless there is a whole lot of it in a confined area.
Photoelectric smoke detectors are best at detecting the type of fire that gives off visible smoke. Burning paper, furniture, wood, ect. are examples of smoky fires.
Ionization detectors will trigger with this type of smoke too, but they are made to detect the non-visible by products of combustion. An Ionization detector is looking for a particle size of 3 TO 5 microns in size. These detectors do a better job of detecting chemical fires, for example. Incidentially: humidity,water vapor, natural gas, freon, and butane will set off ionization smoke detectors.
There are two types of heat detectors. Rate of rise detectors respond when the temperature rises rapidly in a short space of time. Fixed Temperature heat detectors respond when their set point temperature is reached. Both types of heat detectors are labeled: “Not A Life Safety Device” because the response time is much slower than a smoke detector.
The best type of single station houshold detectors use both Ionization and Photoelectric sensing devices. The devices in my house are battery operated, dual sensing smoke detectors made by the Kidde corporation and marketed under the “Nighthawk” label, commonly available at most lumber and haedware stores. while you are there, pick up a plug in type carbon monoxide detector (with battery back up) for each floor of your dwelling. Again, the Nighthawks are the ones I like.
One more thing: Every time the time changes (spring forward, fall back) change the batteries in your smoke detectors. If they are more than five years old, replace them.