What key characteristic does an ionization detector have?

An ionization detector is specifically designed to sense invisible particles that are produced during a flaming fire. This type of detector contains a small amount of radioactive material that ionizes the air in the sensing chamber. When smoke particles from a fire enter this chamber, they disrupt the flow of ions, leading to a change in electrical current. This change is what the detector identifies as the presence of smoke, indicating that there may be a fire.

The ability to detect these invisible particles is crucial because flaming fires typically produce smaller smoke particles, which can be detected by ionization technology more effectively than visible smoke. This characteristic makes ionization detectors particularly valuable in situations where early detection of flaming fires is necessary.

Regarding the other options, ionization detectors do not focus on visible smoke or measure heat changes, which are typical functions of other detection systems, such as photoelectric smoke detectors and heat detectors, respectively. Additionally, while detectors may need maintenance, ionization detectors generally do not require frequent calibration like some other sophisticated electronic devices.