Stealth Boy The RobCo Stealth Boy 3001 is a personal stealth device worn on one ' s wrist . It generates a modulating field that transmits the reflected light from one side of an object to the other making the bearer almost invisible to the untrained eye . History . The technology was developed by Robert Mayflower , based on captured Chinese Hei Gui stealth suits , belonging to the Black Ghost counterinsurgency / terror units . Though the Stealth Boy is more portable and capable of projecting a more powerful stealth field , it has severe drawbacks , as listed below . After the Great War , it was used by the nightkin elite super mutants units of the Master ' s army . In " " , Doctor Henry is in possession of schematics for the Stealth Boy mark II prototype . Experimental even before the Great War , he has managed to recreate one hoping to provide insight into the nightkin ' s problems . However upon asking Lily Bowen , a friendly nightkin to assist with the experiment he is soon interrupted by Keene who demands the schematics so he and his band of nightkin can modify existing Stealth Boys to mark 2 . The Courier then has a choice between talking Keene out of it , killing him or giving him the schematics . Some time after they acquired the Stealth Boy technology , the Brotherhood of Steel experimented with those devices . When the side effects were discovered , the devices were banned and the team disbanded . However , it was not known that the team had already begun to suffer the effects of the device . Thinking the disbanding of their team to be a conspiracy , they decided to steal the Stealth Boys and form a new covert operation called the Circle of Steel . Side effects . Prolonged , repeated usage of Stealth Boys have been found to have unpleasant mental side - effects , causing anxiety , paranoia , wild mood swings , and even schizophrenia and dementia . These effects take a long time to manifest in humans ( the player can use Stealth Boys without any negative effects ) , although they appear only after a few uses when used by Nightkin . As Nightkin were originally The Master ' s elite stealth troops , nearly all of them used Stealth Boys , resulting in all of them suffering from Stealth Boy sickness . Their mental problems vary , but the most common symptom is the development of an imaginary companion or second personality ( similar to Dissociative Identity Disorder ) . Notable Nightkin who suffer from Stealth Boy sickness of this kind are Davison , Tabitha , Lily Bowen , and Dog / God . Stealth Boy usage appears to be addictive to Nightkin , as they go through withdrawal when deprived of Stealth Boys for a long time , becoming more aggressive , short - tempered , and fearful of being seen or stared at by others . Variants . Stealth Boy . Stealth Boys can be found in " Fallout " , " Fallout 3 " , " " , and " Fallout 4 " , although it is mentioned in " Fallout 2 " and its description is present in " " files . The device ' s back story wasn ' t developed until " Van Buren " , the canceled " Fallout 3 " by Black Isle , where it was spelled as StealthBoy to prevent it from being confused with the " Stealth Boy " playing style . It was going to appear in the canceled " " as " stealth girl " , as it was usable only by Scarlet , a female character . Stealth Girl later became a reference used in " Fallout : New Vegas " , as the companion perk given by Lily Bowen , a female nightkin , the perk provides a 200 % increase in Stealth Boy duration . Stealth Boy mark II prototype . This world object is an enhanced Stealth Boy , put through testing by the Enclave during the Great War . It is only seen used by Lily during the quest Guess Who I Saw Today .