Spring loaded syringe guard

I don't like needles. I'm not adverse to pain, but the thought of something that can penetrate my skin so easily gives me the heebie-jeebies. On a serious note, needles contaminated with bloodbourne diseases are a killer. It occurs to me that a spring-loaded guard could protect people from contaminated needles. The guard is pulled back to use the needle and then springs back into place once it has been used. A catch system could make it that once it has sprung back, it is locked in place. The diagram below illustrates (although not a catch as this was too hard to draw!).