About 90% of existing smoke alarms do. They use ionization to react to fires. These ionization chamber smoke detectors contain radioactive material. The radiation source is a small disc, about 3 to 5 millimeters in diameter, weighing about 0.5 gram and made of americium-241 in a gold matrix. Because they are inexpensive, ionization detectors are more common. We decided that radiation wasn't a good idea for our device. You can learn more about the different types of smoke alarms here.
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