Chameleon Arch The Chameleon Arch was Time Lord technology which could modify the biology of an individual , essentially changing that individual ' s species . Connected to a TARDIS databanks via a cable , the arch resembled a headset incorporating a biodata module usually resembling a fob watch . The module was placed on the front on the Time Lord ' s forehead . The watch stored the Time Lord ' s essence and when opened , would return it to the Time Lord . The arch gave the Time Lord a new personality and memories . To ensure that the biodata module would not be noticed , it was incorporated with a perception filter . Using the arch re - wrote a Time Lord ' s cellular biology and was therefore painful . The Tenth Doctor screamed in agony when undergoing transformation into a human . It was capable of altering them both with or without modifying their outer appearance . ( TV : " Human Nature " / " The Family of Blood " ; AUDIO : " The Heavenly Paradigm " ) Function . Some traits of the user ' s true Time Lord self still remained after the use of the Chameleon Arch . For example , John Smith was able to use a simple cricket ball to deliberately cause a complex chain of events to save a mother and her baby from being crushed by a falling piano . Smith also kept a dream journal in which he chronicled memories of the Doctor ' s adventures . ( TV : " Human Nature " / " The Family of Blood " ) heard drums beating in his head all his life , a burden the Master also faced . ( TV : " Utopia " / " The Sound of Drums " / " Last of the Time Lords " ) The Eighth Doctor claimed that destroying a Chameleon Arch while the user was not a Time Lord would render their Time Lord personality and biology irretrievable . ( AUDIO : " One Life " ) Notable uses . There was an account suggesting the Seventh Doctor , prior to his regeneration into his eighth incarnation , made use of a broken Arch to create the fiction that he was half - human to use against the Master . ( COMIC : " The Forgotten " , TV : " Doctor Who " ) The Time Lord who would become Quarren Maguire was a powerful psychic with a great potential to manipulate reality , but he used the Chameleon Arch to escape the Time War as he didn ' t want to fight , hiding his Time Lord self in a locket that he shared with his wife , Rupa Maguire . After the Daleks attempted to track him down , his identity was exposed by Ollistra while he was attempting to escape with various other human refugees in the TARDIS . Lost for options , Maguire opened the Arch and restored himself to his original state , rewriting reality to save the TARDIS and send most of the human refugees to safety - although he left the Eighth Doctor with the company of his new acquaintance Bliss to act as his new companion - while sending the other Time Lords away from the TARDIS . This action also erased his entire human life from history , with the result that Rupa no longer had any memory of meeting him or their marriage . ( AUDIO : " One Life " ) The Master also used the Arch to turn into a human infant to escape the Last Great Time War , after witnessing the Dalek s take over the Cruciform . ( AUDIO : " The Heavenly Paradigm " ) He remained in human form until he opened the biodata module and remembered who he was . ( TV : " Utopia " ) The Ninth Doctor gave a biodata module to Plex . ( COMIC : " The Promise " ) The Tenth Doctor used a Chameleon Arch to change himself into the human John Smith to elude the Family of Blood . ( TV : " Human Nature " ) The Tenth Doctor used a representation of his Chameleon Arch to recover his memories , after his mind was taken over by Es ' Cartrss of the Tactire . ( COMIC : " The Forgotten " ) The Tenth Doctor also briefly considered that Jackson Lake might be a future incarnation of himself under the influence of an Arch . Lake had what turned out to be just an ordinary fob watch . The initials on the back of the fob watch revealed his true identity to both himself and to the Doctor . ( TV : " The Next Doctor " ) Known Chameleon Arches . During the Time War , the extremely psychic Time Lord who would adopt the name Quarren Maguire used a Chameleon Arch to make himself human , fearing his abilities would be used for the destruction of more than just the Dalek s . His biodata module took the form of a pendant . ( AUDIO : " One Life " ) After the destruction of Gallifrey , there were only two known Chameleon Arches in the universe . One belonged to the Doctor inside his TARDIS , though he gave the biodata module fob watch to Timothy Latimer . ( TV : " Human Nature " / " The Family of Blood " ) In light of its later appearance in the Eleventh Doctor ' s drawing room ( GAME : " TARDIS " ) , he seemed to have either recovered it or had duplicates , as the Ninth Doctor gave a modified one to Plex that broke down by the time the Twelfth Doctor retrieved it . ( COMIC : " The Promise " ) The other was in the possession of before he left the end of the universe for the 21st century . ( TV : " Human Nature " , " Utopia " )