I just think it is odd that the second my one piece of toast get dark brown my smoke detector is sounding the alarm but when I have a ton of friends over and the place looks like a fog factory it doesn’t even make a peep.
Vex
I can’t be too sure about this but in my days as a firefighter, I remember something about some smoke detectors that are activated by heat more then smoke. I have the same problem with my smoke detector, I smoke and nothing happens, I bake cookies and every one in the house goes off. I’m not a very good cook 
How smoke detectors work. Short version–there are two different kinds. One kind is activated by a photoelectric cell, which detects the way a light shines through smoke, and which are better at detecting big smoky fires.
And there are ionization detectors, which is what most home smoke alarms are, which work by–um, I don’t get it either, but you can read it about it at the link. Something to do with americium and ions.
Anyway, this is the kind that’s better at detecting the smaller amounts of smoke in a hot house fire.
I have no idea why burning toast would set off your alarm and a houseful of smoky friends wouldn’t, but I bet that someone will be along in a minute who does know.
BTW, it’s sprinkler systems that are triggered by high heat, not smoke alarms.
If you get eough smoke in a small enough volume then ciggy smoke will set off the detectors.
Some sensors are operate on the rate of temperature rise, so that if the heat of the room changes slowly to a high level or it has a high ambient temperature, like a boiler house, they won’t go off unless there is a sudden change.
Great question. Here is my best guess. IIRC, the smoke particles in cigarette smoke are extremely small. I think this very small size may make them less likely to absorb the alpha particles (helium-4 nucleus) which are generated in an ionization detector. I suspect that your burnt toast is emitting much larger smoke particles.
Nah, I’ve smoke detectors go off in almost every apartment and house I have lived in due to excessive cigarette smoke. Maybe 'cause I always bought the cheap ones.
rsa, I ALMOST bought that explanation til I remember the morning I was apartment sitting, rushed out of the shower nekkid to fight the fire, only to realize that the noise scaring me half to death was directly out the door of the bathroom and had been set off by steam.
How much larger are water particles than cigarette smoke particles?
True, in my research I read that steam can set off a detector. If I understand correctly, two things can set off a smoke detector.
(1) Something absorbs the alpha particles which decreases the number of ions created, thereby setting off the alarm.
(2) Something (usually smoke) “neutralizes” some of the ions which causes the alarm to sound.
Enough of almost anything will set off a smoke detector. But there must be some reason that a small amount of burnt toast will set off an alarm when a “visibly” greater amount of cigarette smoke does not.
So without further ado, here is my new, improved theory.
Apparently cigarette smoke particles are actually much larger than most other types of smoke particles. Perhaps this larger particle size makes the smoke more visible even though it is in fact of a lessor quantity than the smoke which sets off the alarm.
I figure if I keep guessing, I’m going to get it right eventually 
I think this issue needs some serious grant money thrown at it so we can have the straight dope!
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.
Wah!! An actual tech person shows up in a thread!
Who knows how to 'splain things–in English!
And can type!
Wah! 
[sub]probably just a fluke[/sub]
Thanks for the replies guys. I did conduct a small experiment and blew as much smoke as I could directly into the detector and it set it right off. PS- Those plastic wrap things that look like shower caps work well to cover up smoke detectors when your really cooking in the kitchen.
longhair, I couldn’t have said it better myself. Granted, I’ll probably curse your name at the next trouble alarm I’m on, since you techs apparently have a hard time with that whole ground-fault thing (I hate that light).
friend KCB615,
Our company’s trouble calls usually go to me, and I hate that light too. It is amazing, however, how many of those trouble calls turn out to be low battery voltage. (I get a 10% commission on sales, and love to install new batteries)
The three word phrase that chills my blood: “Intermittent Ground Fault” Especially in a large system, late on a Friday afternoon. I live for those little green LED’s.