I used to be as a kid. I'm not so much any more, but I still find them interesting. My favorite is the Wake 'n Warn / Family Gard ones that were sold during the 1990s. I used to see them everywhere, and I personally had two of them as a kid. And way back in the day Dad had a very old smoke alarm, one that made a squealing sound, rather than a beep. It no longer exists, but I think now that it may have been the original First Alert. I think Dad once told me he bought it in the 1970s, so it must have been. It last worked in the late 1990s - he would occasionally hit the test button on it to entertain me. After that the battery died and was never replaced. Too bad I never thought to grab it before his house was knocked down.

Over the summer I found a mint-in-box Wake 'n Warn at my grandparents' place. I've uploaded a video of it here:

https://www.youtube.com/watch?v=yBzfUrQ4qs8

Trent

The one i grew up was the older vulcan fire/burgular alam, as it is compleatly mechanical and very annoying
Bell like sound comes out of it when u press test
It will ring like 1 hour long until it became unwound.

I think I have a couple of Wake-n-Warns.  They were basically the same unit as a basic First Alert.

I too have had an interest in them over the years.  First ones I remember were in the house that I grew up in.  They were unusual in that they were square, with a red test button in the middle of the cover, and they made a steady honk sound instead of beeping.  As a little kid (around 3) I was afraid of it.  Used to have one in the back hall and one between the kitchen/dining room and living room.  Don't know who made them, and the only place I ever saw others like that were the neighbors 2 doors down had the same ones.  I want to say around 1990 they were replaced with round First Alerts, which were similar to the Wake-n-Warn except they had the flashlight tester.

More common in the early-mid-80s was the large round First Alert.  I have one somewhere that still works.  Some friends also gave me a really old photoelectric smoke detector that I think was from around 1971.  Was Sears branded, used a flashlight bulb as a light source.  Of course, it wasn't battery operated and had to be plugged in.  With the cover removed, you lifted the contact off the shell of the bulb, causing the bulb to go out and the alarm to sound.

So after a quick Google search and some good luck, I found the bane of my early childhood, the GE Home Sentry.

http://youtu.be/7TFA_ilX7mc

Oh god, that would have terrified me too as a kid. Actually never mind, it would still terrify me today. 

Several years ago, around the time I joined this site, I went to visit my brother in Maryland.  In the stairwell of this house, I found this old general electric smoke alarm.  I decided it was photo worthy, but didn't realize it was a newer version of the ones I grew up with early on.  Shoulda nabbed it...

I was never into them but remember being afraid of the "chirping" of one in my late mother's house when the battery would start to get low.
I have a "taking" First Alert that sometimes goes off for no reason scaring the cr@p out of me at 2AM!

We used to have a talking First Alert smoke and CO detector that the government installed for us back when we still used an oil furnace to heat the house. It plugged into the mains through a proprietary plug, and had a 9V battery backup. I went to change the battery in it one day, and it just completely broke on me for no reason. I unplugged it, changed the battery, and when I plugged it back in it would just emit a solid beep. Don't know what happened, but it never worked again.  So government workers replaced it with a Kidde non-talking non-CO mains-only detector.

I've never witnessed the low battery alarm of a smoke detector go off in the daytime - it's always in the middle of the night. So annoying...

It goes off a bit easier in the darkness:
The sensor consist of a LED and two light detectors in a detection chamber. One detector is paced so, the light from the LED lands on it, the second detector is "behind a corner", so no direct light from the LED can reach it. If a smoke enters the chamber, one of two things (or both) happen:
- The light blocks part of the light, so the "normally lighted" sensor see less light
- The light is scattered, so the "dark" becomes illuminated by the scattered light
When one of these conditions is met, the alarm go off. Sometimes it is done by just comparing the current of both detectors (the "lighted" is made with intentionally lower sensitivity) and when the "dark" sensor passes higher current than the "lighted" one, the alarm is triggered. Sometimes the LED current is regulated to have the "light" sensor illumination constant.
All this does not work continuously, but in short pulses with about a minute repetition time, so the battery drain is minimized.

Normally the battery check is done by measuring the amount of the light landing on the "illuminated" photo detector. As the battery get weaker, the LED current drops and that become detected as a weak battery and a "weak battery" alarm (usually the same as the main alarm) is triggered.
ow as nothing is perfect, the "lighted" sensor tend to be influenced by the ambient light, so during the day lower LED current is sufficient to keep it "happy". With the "constant illuminated level" it means the alarm starts to draw higher current at night, so as the battery get weaker over time, it trip the low battery warning during that night.

Makes sense. But now how does that explain the same phenomenon with ionization-based detectors? I suppose maybe coincidence...

I don't know, how the ionization types exactly work (the photo current induced ionization plays a role?) and how the battery check is implemented there...

I have a bit if interest in them, just kind of cool all the varieties.  They are kind of neat to see and hear.  We have an older one in our house still in use, it may be early 2000s IDK for sure.  Funny thing is it had set there untested for a long time, so I suddenly decided to test all the ones in our house, I went upstairs to that one (in my parent's room) and tested it (it does a constant beeping tone) and as I went downstairs I heard the low battery chirp.

Also the GE Home Sentry is awesome.  It would be neat to have one put up in our house.

Ionization detectors use a small radiation source, a cathode connected to a regulated power source, and an anode connected to the monitoring circuit.  The radiation source ionizes the air in the chamber, allowing a small current to flow from the cathode to the anode.  Combustion products don't ionize as easily, causing smoke to act as an insulator.  When it enters the chamber, it blocks the current flow, tripping the alarm.  The anode maybe a plate or screen inside the chamber, or in some designs, maybe the metallic shell of the chamber.  The test button simply shorts the anode to ground, causing the monitoring circuit to see no current and tripping the alarm.

Ionizing detectors are generally more sensitive to combustion products from fast flaming fires, as well as similar substances like fine dust and steam.  Photoelectric detectors are generally more sensitive to combustion products from slow smouldering fires.

Slightly off topic, but my university had the oldest buildings wired with a very old 6 volt fire alarm. The bells were wired differently than the actual standard (series/parallel difference, I don't remember). The panel was located in the basement and had magnetic switching levers that were held up by an electromagnet. When the circuit sent an alarm signal (smoke detector or pull station) the current to the electromagnet was cut and the lever fell down onto a contact bar that energized the bell circuit. To reset, you had to first reset the tripped device (pull station etc.) and then lift the lever up to the reenergized electromagnet. The levers were all numbered (1 to 15 if I remember correctly). All this was locked in a red metal panel. Almost as big as the panel was a cabinet housing backup batteries. All this was removed about six years ago when all campus was converted to computer based fire protection, all interconnected to the night watch station.

Wow, that sounds like a pretty neat system!