Final answer:
An ionization-type smoke detector is activated by invisible products of combustion such as smoke particles. It contains a small amount of the radioactive element americium-241 which ionizes the air between two electrode plates. When smoke particles enter the chamber, they interrupt the flow of ions and trigger the alarm.
Step-by-step explanation:
The type of smoke detector that is activated by invisible products of combustion is called an ionization-type smoke detector. These detectors contain a small amount of the radioactive element americium-241, which emits alpha particles that ionize the air between two electrode plates in the detector. When smoke particles enter the chamber, they interfere with the flow of ions, reducing the conductivity of the air and triggering an alarm.