MARTIN BOND / SCIENCE PHOTO LIBRARY MARTIN BOND / SCIENCE PHOTO LIBRARY
Radioactivity warning symbol in smoke alarm. Close up of the inside of an ionisation-type smoke alarm, showing a trefoil radiation symbol and details of the alarm's radioactive source. The radiation produced by this radioactive source ionises the air between two charged metal plates, causing a small flow of electricity. Smoke disrupts this, triggering the alarm. The labelling on this smoke alarm states that it contains 0.9 microcuries (Ci) of the radioactive element americium-241. This is given at right in a different unit, as 33,000 becquerals (Bq). The central circular grey area (with the symbol and contents information) is 24 millimetres in diameter.
Model release not required. Property release not required.