12月20日，平谷线马坊站至马昌营站高架区间施工现场，一段桥梁上部结构正在进行施工转体作业。新京报记者 王贵彬 摄
Optical-based smoke alarms use light instead. They are slightly better at detecting the large smoke particles created by slow, smouldering fires. When such particles enter a chamber in the device, they scatter light from a small light source, which is then picked up by a photoelectric sensor.
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"I'm going to keep sticking at it until I get a home," he says.
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