smoke - fire detection

I'm looking for a sensor to detect smoke or possibly fire. i found some sensor IC's that require a lot of external components an a lot of calibration. Does anybody here know of a more "of the shelf" solution" for a detector that will interface to Arduino, and require a minimum of extra components and calibration ?

One alternative i'm considering is hacking into a standard smokealarm. It should be possible to find somewhere in a standard smoke alarm (for instance the piezo / speaker) where Arduino can detect that the alarm went of.

Thanks

AFAIK, a smoke alarm is just an airduct with a led or any light emitter facing a light sensor of any kind. When smoke enters the devices, it limits the amount of light going to the sensor which, under a certain threshold, starts the alarm. I think the most important point is to find a way to make it completely dark to prevent false readings due to ambiant light.

Most smoke detectors use a combination of light detection and ionisation to detect smoke. I think all newer ones have a radioactive source in them. Remember the radioactive boy scout? http://en.wikipedia.org/wiki/Radioactive_boy_scoutHe built a fast breeder nuclear reactor in 1994 in his backyard shed by collecting small amounts from household products, such as americium from smoke detectors.

In theory it sounds easy to tap the peizo alarm line from a smoke detector, but I don't know if I'd be too happy to start taking them apart.

Most smoke detectors use a combination of light detection and ionisation to detect smoke.

Afaik, most smoke detectors use one or the other, not both (there are some, but they're basically two smoke detectors in one package at a higher price than buying 2 separate units).

In an ionisation alarm, the radioactive material electrically charges the air in the detector's chamber, and this electric field can be detected. Smoke particles deionize the air, and the alarm goes off. Generally they're much better than photoelectric detectors because they detect a much, much smaller concentration of smoke (think how smokey a room has to be for a cubic inch to look hazy). But generally you should have both installed.