A null field generator was a device that created fields capable of deflecting many sorts of transmissions. Sounds and radiation on one side of a null field could not penetrate to the other.

Close to the time of his death from old age, Angelo Colasanto kept a null field generator salvaged from the ruins of the Torchwood Hub hidden under the floor directly beneath his bed. When Jack Harkness approached, the device activated, shielding Colasanto from the effects of Miracle Day, preventing him from becoming immortal like the rest of humanity and allowing him to die. After the device was discovered by the CIA in Colosanto's mansion, Harkness reprogrammed the generator to nullify sound around the device so he could talk privately with agents Rex Matheson and Esther Drummond about the danger it posed to 21st century Earth. With the ability to hide almost any event from detection, Harkness warned that the temptation to kill and destroy on any scale — all in secret — would lead to a devastated and barren future. Before escaping from the mansion, Harkness slipped a panel from the generator into a coat pocket, claiming that without that single panel, the device would not function. (TV: End of the Road)

Community content is available under CC-BY-SA unless otherwise noted.