# Smoke alarms that run on AA or AAA batteries?



## bltkmt (Nov 3, 2009)

Seems like most models only run on 9v batteries...not sure why? Now that Eneloops have taken off in the market, are there any smoke alarms that could use rechargable AA or AAA batteries?


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## JohnR66 (Nov 3, 2009)

Using rechargeables in a smoke detector would not make much sense. For one, an ordinary 9 volt battery lasts for years in them and that may be longer than the shelf discharge rate of the LSD cell anyway.

Secondly, A rechargeable has more of a steep voltage drop near the end of discharge as compared to an alkaline battery. It could be possible to miss the low voltage signals and go unprotected.

The venerable old 9volt transistor radio battery seems to be synonymous with smoke alarms. It is one of its last stands as most products use AAs AAAs or some form of rechargeable battery. Not sure why the high voltage of a 9 volt battery is needed. perhaps it helps with the current flow in the ionization chamber. I recall the old detectors from the 70's requiring a long cylindrical 12 volt battery.


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## Diesel_Bomber (Nov 4, 2009)

All the new smoke detectors I've seen recently have a built in non-replaceable lithium 9v that lasts 10 years. You're supposed to replace the detector every 10 years anyway, so it makes sense to me. I wouldn't bother with rechargeable batteries.

:buddies:


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## Illum (Nov 4, 2009)

Diesel_Bomber said:


> All the new smoke detectors I've seen recently have a built in non-replaceable lithium 9v that lasts 10 years. You're supposed to replace the detector every 10 years anyway, so it makes sense to me. I wouldn't bother with rechargeable batteries.
> 
> :buddies:



eek...I hope these manufacturers know that the 241Am embedded in those alarms has a half-life of 432.2 years.

I'm pretty sure existing alarms will tell you change it every month or every 6 months. I run them down in my pak-lite when they do chirp:twothumbs

Smoke alarm batteries need that high voltage to sound the alarm when the photoreciever does close the circuit, but 99.99% of the time they die from the quiescent current drawn from the circuit. I'm pretty sure its in the <100 µA range because the PP3 [or the ANSI standard 1604A] batteries in alkaline form has only approx 550mah of juice, Carbon-zinc as about 350mah, but thats a conservative estimate. 

It sounds perfect for carbon zinc cells because thats what they're designed for: low current draw, long load time. Alkalines are half and half because they tend to [in my observation with 5 kidde alarms in the house, 3 of them beside my lithium pile] self discharge faster than the carbon zincs [and therefore chirp sooner] within the same amount of time before I change it [~1yr].

No point at all going for rechargeables because NiMH 9Vs are like ~150mah [if even close]

I suppose you could build a smoke alarm circuit [using the photodiode and cross screen method, not the method involving 0.9 μCi of Americium-241] using single cells, but good luck finding a low voltage, low current buzzer that can sound loud enough to go past a couple closed doors. Even if you do manager to take it that far, the quiescent [standby] current with the photodiode running will deplete the AA/AAA in short order before the buzzer even has a swig of the action. If the batteries do get depleted beyond the ability to inform you that their depleted, then your really in trouble.

I think the smoke alarm is the best standby circuit available, theres a reason why smoke alarms from the early 90s looks the same as ones made in the late 90s: it can't be improved anymore:shrug:

If you really want to do some tinkering, heres a photodiode circuit
*



*I like your idea though, I hope one day I can do the same and build a smoke alarm circuit that runs on CR123as, having not only a buzzer but a built in thrower light so I can yank it off the wall and use it to escape. *
*


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## LEDMaster2003_V2 (Nov 4, 2009)

Alarms the run on AAs?

Kidde CO/Smoke combo (x3)
Kidde Wireless Smoke Alarms (x3)

First Alert OneLink alarms (x2)
First Alert SCO7 (x2)

Older alarms:
SmokeGard 800A, 800C, 801A (x6)
Teledyne D-1 (x6)
Amway E9644 (x6)


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## Kestrel (Nov 4, 2009)

Wow Illum, good info! :thumbsup:


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## Illum (Nov 4, 2009)

LEDMaster2003_V2 said:


> Alarms the run on AAs?
> 
> Kidde CO/Smoke combo (x3)
> Kidde Wireless Smoke Alarms (x3)
> ...



nice info!
I haven't noticed there were AA alarms, maybe I need to look closer on the shelves.
:thanks: for the heads up

6? gee... that's like paralleling 4 9Vs, what do they have? subwoofers?:thinking:


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## LEDMaster2003_V2 (Nov 4, 2009)

And actually some wireless smoke detectors for security systems _do_ use CR123s! There was even one model which took _ 8 *C-size*_ batteries!oo: Some older units used 10.7, 11.2 or 12.6 volt mercury batteries, which were up to $15 a pop! There's even a detector in Europe (now invading the US by way of being preinstalled in some new RVs) which uses 3 coin-cell batteries.


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