A Geiger counter was a piece of technology involving radiation that made a ticking noise. The First Doctor considered it to be advanced technology. It included a needle on a scale that could reach a "danger point". (TV: "The Survivors")

Humans used the technology. In 2013, Kate Sherrin monitored the changes in radiation on the shoreline of Ambermouth using a geiger counter. (AUDIO: Eldrad Must Die!)

A Geiger counter was used on Recovery 7 when it was brought back to Space Control. It detected levels of radiation in the ship's interior which were so high that its setting was on maximum. (TV: The Ambassadors of Death)

The First Doctor had such a device, but it broke during his first travel with Ian and Barbara. (TV: An Unearthly Child)

The Daleks made use of one, and the Doctor, Susan Foreman and Ian once encountered it on Skaro. It showed them the excess radiation there, which resulted in a jungle being turned to stone, the soil becoming barren, and sickness among the three. (TV: "The Survivors")

The equipment of the soldiers of the Combined Galactic Resistance was provided with such technology. It helped to diagnose a radiation leak as the cause of malfunctioning of a Dalek. (TV: Into the Dalek)

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