The Dresden Files touches on this with some of their wizards.
While wizards are aware of 21th century tech, they just aren't aware of the finer applications. eg. It doesn't occur to them that someone could use a sniper rifle against them even though the main hero carries a gun.
To be fair, wizards have a disrupting field that prevents them from using anything beyond 1940's tech or more complicated that a gun with a good deal of safety or reliability.