A cliche idea--people can have all of their identification, medical & financial records, etc, encoded into a bar code that gets tattooed on their wrist. Most people think it's great; a few dissenters worry about the information being stored in it and the freedom they're giving up in exchange for some vague promise of "safety." Poor execution in clumsy, exposition-heavy dialog and only the slimmest character development. Not recommended for anyone for any reason--there are plenty of other books* who use this same idea and do it better. 
 *LJ Adlington's Diary of Pelly D, which while not great was better than this POS; Janet McNaughton's Secret Under My Skin, for examples.