Before anyone thinks I’m crazy, hear me out. The Sonic Screwdriver could be very similiar to how the plasma pistol works. However, it disables shields and weapons for a short period of time. In order to use it, you would point it at something (Elite) for a couple of seconds. It could have a similiar firing sequence to the Spartan Lazer. After you fired the sonic screwdriver, the Elite’s shields would go down and his primary weapon would not work. He could still throw grenades, run away (I’m looking at you, Reach Elites), or use a secondary weapon. The screwdriver could also be used to disables vehicles.
Since the screwdriver would only disable things instead of directly harmining emenimes, it would be balanced. Becuase it would be very powerful, it would also have a limited amount of charges. The screwdriver could recharge its batteries by fully draining the user’s shields, but only by 1 charge. Finally, the screwdriver could be used on the environment. If its used on a wall w/ circuits, a light, or near a door, the screwdriver would overload the circuits and make sparks fly that could disorganize enemies.
Also, I’m a huge Doctor Who fanboy >.>