Military helmets and plate carriers are specific items best used by military personnel doing specific military stuff.(combat operations) They are heavy and uncomfortable to wear at the best of times. Helmets are designed for shrapnel protection and only block bullets in the movies. If shrapnel is a concern where you live you have bigger problems. A good set of plates may or may not stop a projectile depending on caliber and angle of strike. If you were shot with the average sized rifle round (even a hollow point) wearing a plate and lucky enough to not have it go through you will still most likely need medical aid very quick as severe bruising and broken ribs/internal bleeding is very likely.

Personally I feel that a self defense firearm would suit you better in this kind of scenario. That's a topic for other forums I guess.