Depends on model. Almost all older ones does (using radiation from the isotope to electrically charge smoke particles that pass through, which then can be detected by a sensor).
The A-241 does not charge the particles, it ionizes the air in a small chamber that allows a steady current. Any smoke particles disrupt these currents to set off the alarm.
Depends on model. Almost all older ones does (using radiation from the isotope to electrically charge smoke particles that pass through, which then can be detected by a sensor).
Many newer ones are optical.
The A-241 does not charge the particles, it ionizes the air in a small chamber that allows a steady current. Any smoke particles disrupt these currents to set off the alarm.