Head chip
From Tardis Wiki, the free Doctor Who reference
The head chip was the "type one" brain chip, a data gathering device used to access screens, available for 100 credits aboard Satellite Five by the year 200,000. Inserting into the back of the human skull, the head chip was small enough to be invisible, causing no scarring. Beyond that was the "type two" infospike. (TV: The Long Game)
