Burn by Walter Jury and Sarah Fine

Burn takes up where Scan, the story of a boy's fight to protect his father's invention, the scanner that can tell human from alien, leaves off.  The scanner is now in the hands of the H2 (alien) forces, but the enemy needs Tate to decipher his murdered father's coded files on how to use the technology and save the planet. Burn is a rollercoaster of a book, with Tate, a teenage version of television's MacGyver, struggling to outsmart his foes while evading capture himself.  There are action scenes galore, betrayals at the highest levels in the Fifty (the humans), arson, torture, and discovery of a new, even more lethal threat to earth's survival.  Impossible to put down.