The Armour and Forcefield traits assume that a character using them is completely protected. Some armour, such as bullet-proof vests, only cover the torso, while both antique and futuristic versions of a hand-held shield only protects its bearer from frontal attacks.
As a Minor Bad Trait, any protection offered by the Gadget only covers 2/3rds of the character (perhaps only covering the front and sides). Opponents may bypass such protection by taking a -4 penalty on their attack rolls; a fantastic success on a regular roll also bypasses the protection. As a Major Bad Trait this cover shrinks to 1/3 (like a medieval round shield). Opponents may bypass such protection by taking a -2 penalty on their attack rolls; a good success on a regular roll also bypasses the protection.
Characters with this Bad Trait are effectively unprotected from area-based attacks that could wrap around the covered area. The Gamemaster may adjudicate this based on the particular circumstances of a situation (e.g. a character with 2/3 coverage can probably prevent being hurt if a grenade explodes in front of them, but a bomb dropped from the sky will probably bypass any shields).