Speaking of Orwell…As mentioned (either here or in other similar threads), I have a Nest t-stat and Nest smoke detectors. I like the nest system because of the smoke detectors sense CO (or smoke) they’ll shut down the furnace as a precaution. OTOH, Google owns nest and all of these items have motion detectors. Google not only knows if I’m home, if I’m sleeping, if I’m not home, when I’ll be expected home, but on top of that, they even have a pretty good idea as to where in the house I am.
Touche! The industry (in general) prefers to use “nuisance alarm” because “false alarm” suggests that the detector malfunctioned. In many cases, the detector actually reacted to an environmental condition that is virtually indistinguishable from products of combustion. For example, heating bars are turned on in the Fall and burn off the dust that has settled on them during the Summer. Or someone sprays an aerosol insecticide near the detector. Heck, one of our biggest problems is when a humidifier in an air-handling system starts spraying water into the airstream.
So, yeah, it’s newspeak, but probably a bit fairer to the manufacturers.
thanks for this. the condo I live in apparently was built (in the 1980s) with two hardwired detectors, one in the garage linked to another in the entrance hallway. Last year the one in the garage falsed (causing the hallway one to go off too.) I pulled the (30-year-old) detector off of the garage ceiling and found it absolutely packed with dead bugs. So I chucked both of them and replaced them with a pair of linked, hardwired dual sensor (ionization and photoelectric) detectors. A week later the garage one falsed again, and I found a gnat had crawled in to the photodetection chamber and set it off. So I pulled the one out of the garage altogether. so it sounds like I’m ok on that as far as code goes? I’ve also heard that one problem with ionization detectors in garages is if you start a car/motorcycle inside that can set them off.
Ionization detectors are very sensitive to certain fumes and gases. Anything that interferes with the current passing through the ionized air in the sample chamber will set them off. For this reason, they are very good at detecting products of combustion common to burning plastic and similar materials. In fact, the most common use for them nowadays (other than in homes) is to detect overheating/burning in wiring assemblies (electrical cables). We rarely use them for open-space protection or in air ducts.
Photoelectronic detectors rely on light (IR) being scattered or obscured by visible products of combustion. The airborne particles are usually in the >= 5 micron range. A well-tuned engine that is not emitting visible smoke will not usually set them off.
There are actually two different UL standards for spot-type smoke detectors. One is for household warning units (the typical type used in a home) and the other is for system-type detectors (normally used in commercial applications, but can be used in homes if you have a fire alarm control panel). Both ionization and photoelectronic units are tested in the identical manner, depending on which standard is applicable, so it doesn’t really matter too much which you choose. EXCEPT…ionization detectors will probably give you more nuisance alarm problems.
I’m not a big fan of dual-technology units, as they don’t really give you much additional protection and the ionization part of the unit will probably be more prone to nuisance alarms. YMMV.
TL;DR: Smoke is your biggest enemy. Visible smoke is easily detected by photoelectronic smoke detectors.
Question not to me but, IMPO,
The question is why was a smoke detector installed in the first place? Was it required by code at the time and if so, what does the current local code require in attached garages for your type of building? Without knowing specifically where your condo is located as well as the sq. footage, amount of floors, number of sleeping areas etc., is is virtually impossible to say of you are “ok as far as code goes”. I assume there is a corridor in your residence that leads to this garage and if so I would stress that there should, at the very least, be a smoke detector in that corridor. I believe the one you indicated as being in the “entrance hallway” is in that location so that should be ok. Ideally this device as well as the ones outside the sleeping areas would have the ability to detect carbon monoxide as well.
Virtually all types of smoke detection principles are susceptible to false alarms due to exposure to vehicle exhaust so it’s not a matter of photoelectric vs. ionization but rather smoke detection in general.
Thank you to ZonexandScout and Longhair75 for well-written information from experts in their field. It makes some of my household smoke detector issues make a lot more sense.
How weird. I found this thread yesterday. Today, for the first time, my alarm decided to go off while showering. I must’ve showered with the door open (bad ventilation, aforementioned toddler) almost 300 times since I got it with no issue. USI Ionization.
I live in a very low humidity environment. Do these go off at an absolute humidity level, or after rapid change in humidity?
Ionization detectors get very funky in high humidity (about 92%-100% RH). Think of the two air chambers in the unit as being on a sort of balance scale. In the absence of smoke, they should conduct current equally. When something interferes with the current in the sampling chamber (the one that has vents and is open to area air), the electronic circuit senses the imbalance and the unit goes into alarm. All kinds of airborne particles, vapor, and chemicals can cause this. Ideally, the unit will just respond to smoke, but this isn’t what happens in the real world.
Ionization detectors are typically less sensitive to larger airborne particles (>= 10 microns or so) because they don’t affect the current flow as much as smaller particles do. When you get “fog” from your shower, it is really a combination of two things: water vapor and water droplets in suspension. The water vapor is usually less a problem than the water droplets. Get the “right” size water droplets and you have an alarm. Many factors (ambient temperature, air currents, how long you showered, etc.) can have a significant impact on the size of the droplets.
Relative humidity is much less a problem for photoelectronic detectors because water vapor is basically invisible. (If clouds were just water vapor, we couldn’t see them.) But the detector will react to water droplets of just about any size because they scatter or obscure IR light, just like the fog in front of your car headlights.
Short version: Water vapor and “fog” are bad for either type of unit, but for different reasons.