In particle physics, gaseous ionization detectors are particle detectors which detect the presence of particles. If a particle has enough energy to ionize a gas, the resulting electrons emitted can cause a current flow which can be measured in different ways. Examples are Ionization chambers, Proportional counters and Geiger-Mueller tubes.

Geiger-Mueller tubes are the primary components of Geiger counters; as the gas ionizes a cureent is able to pass through a potential difference between two plates. The peak in current is passed through an audio device producing the clicks of the Geiger counter. Smoke detectors work on a similar principal; a bit of radioactive americium is placed so that it maintains a current between the two plates. If smoke gets inbetween the plates where the ionization is taking place, the ionized gas can be neutralized leading to a reduced current. The decrease in current triggers a fire alarm.

Proportional counters work on a similar principal, but by using a smaller potential differnce between the electrodes, the determination of ionization energy is allowed for.