SMOKE ALARM QUESTION.

when you press the test button on a smoke alarm to test that it is functioning.

dose it just test the battery is powerful enough to sound the alarm.

or dose it have some way of testing the smoke detector circuit is working.

I mean the smoke sensor.

I think their are two type OPTICAL and INONISING sensors.

I have seen them tested with a can of smoke, or a special type of match.

regards.

It's just a test of the circuit for enough power to sound the alarm.

Funny thing about smoke detectors. Ten years ago I moved into my house and bought 3 new smoke detectors. We had a child last year and I bought two more of the same kind (First Alert). Yesterday, I checked the expiration dates on all the detectors (stamped on the inside of the detector) and found that the ones I bought in 1996 expire this year and the ones I bought last year (2005) have an expiration date of 2008. I checked First Alert's web site and they claim ten years on the smoke detectors. So the two I bought last year have been sitting in a warehouse for 8 years? That just doesn't seem right.

I didn't know smoke detectors have an expiration date. I wonder why they do. I have read that the test button on newer detectors test more than the battery.

Anyway you can always test them with smoke. In the old days we didn't buy smoke in a can, but I guess I'm just old fashioned. A cigarette or candle ought to do it. The ionization type and the photo detector type may require a different technique.

I can tell you that a cigarette is one of the recommended ways of testing a carbon monoxide detector. It works very well indeed. On the other hand my kerosene lamps don't produce any detectable carbon monoxide, and I'm guessing a candle normally wouldn't either.

As far as I have been told the test button is not a true test of the detector.
Most fire alarm techs that I have seen carry a can of smoke to set the alarm off and sometimes a can of air! to clear it again.
This is meant to be for Ionization and Photo electric types and not of course for heat sensors ( I think they are K type thermocouples ) 60watt light bulbs do the trick for that just hold them close and wait for the detector to trip (usually mounted in a cowl to cover the detector and bulb).

The alarm takes many times more power to sound than the detection circuit requires to run. If the alarm can be triggered and sound produced, then there's sufficient power to run the detection circuit.

eluminator said:

I didn't know smoke detectors have an expiration date. I wonder why they do. I have read that the test button on newer detectors test more than the battery.

Click to expand...

well, optical alarms doesnt matter, they use essentially LEDs. the ionizing ones, however, uses the radioactive decay of Americum 241. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the Americum knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively-charged oxygen and nitrogen atoms are attracted to the negative plate and the electrons are attracted to the positive plate, generating a small, continuous electric current. :naughty:When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The drop in current between the plates triggers the alarm.:huh:

I think its something to do with the decay of the isotope correlating to the expiration date.... :thinking: if i remember correctly [chemistry soo long ago] the half-life of Am-241 is around 400 years...so that doesnt quite explain it...

Lightmeup said:

It's just a test of the circuit for enough power to sound the alarm.

Click to expand...

Yep, indeed!
If you want to test the functonality of it, insert earplugs and just set something on fire under it and see if it functions.

This reminds me that I should get a new battery for my smoke detector...

I have an talking combined, smoke and carbon monoxide detector.

It shouts, FIRE FIRE FIRE, or CARBON MONOXIDE DETECTED.

It also tells you when the batterys are low.

regards.

TinderBox (UK) said:

I have an talking combined, smoke and carbon monoxide detector.

It shouts, FIRE FIRE FIRE, or CARBON MONOXIDE DETECTED.

It also tells you when the batterys are low.

regards.

Click to expand...

An dectector like that will burn through a 9V faster than the typical "kiddie" detectots that come in packs when you buy a fire extinguisher...

it uses 3 x AA batterys, and i have only replaced the batterys once in 2 years.

regards.

A friend moved into a house with a gas furnace so I got her a Nighthawk gas detector unit.
We would test it by farting into it. Even a cupped hand brought from the posterior and held up to the wall unit would set it off.
We tested it quite often. Farts from other rooms had no effect.. I tried...and tried..

eluminator said:

I didn't know smoke detectors have an expiration date. I wonder why they do.

Click to expand...

Ionization detectors use a radioactive isotope (americium-241), which will ionize an air/smoke mixture that has enough smoke in it. When the chamber that contains the americium ionizes, it conducts electricity, and "turns on" the alert.

As a radioactive product, americium isotopes have a half-life, but the half life is a lot longer than 10 years (it's somewhere in the 400 year range but I don't recall the exact number), so there may be no real reason to replace the detector other than liability and the manufacturer's desire to sell more detectors. How can you be in the business of making money if people only buy your product once?

Some years ago while I was in college I saw a whitepaper on how another university tested ionizing detectors against photoelectric, and the photoelectrics proved to be superior in terms of sensitivity to smoke (ie. gives an earlier alert).

Surprised I didn't see this!
I collect smoke detectors!!

Anywho, yes, Ionization (Ionisation) alarms are only truly reliable for 10 years. After that the sensor loses its ability, or sometimes it becomes oversensitive (I have a couple that will trip if hit by a breeze!) The older alarms actually used electromechanical horns which really sucked the battery up when they sounded, since they use an electromagnet to sound. The newer ones have piezo elements which are alot less power consuming, but are so high-pitched, that it has been found that many older citizens cannot hear them. Also, no, I don't plan on making a dirty bomb. The NRC says that it would take at least 10,000 ion chambers to create even a low-level dirty bomb. Using a spray is much better than using the button. Some older models actually could be only tested by smoke, no button anywhere on the unit.

Check this.

I've never understood why the batteries on these things are replaceable at all. They should come with a lithium 10 year 9v insternally and when it's used up they are at the end of their life anyway and you just replace the whole unit. How much money does the charging circuit cost and complexity of construction and whatnot? When they could just include a better battery to start with. I know that lithium 9v's are expensive, but not when amortized over a 6 to 10 year life

I deal with at least 5 different manufacturers of commercial smoke detectors and not one of them has an expiration date.
They are, however, required to be tested annually.
I would suspect that the expiration date on residential smoke detectors has more to do with bureaucratic greed and corporate CYA than any measurable life expectancy.