There are two main types of smoke alarm tech, says Raman Chagger, principal consultant at BRE, the Building Research Establishment. Ionisation-based systems use a tiny amount of radioactive material to charge, or ionise, particles in the air which flow between two small plates. Should smoke interrupt that flow of charged particles, the alarm goes off.
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Watch: Pakistan releases footage it claims shows strikes on Kabul
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Fake news is everywhere, but what is it and how can you spot it? Watch our video and read useful tips on how you can spot fake news quickly!