an outer housing, a generally longitudinally extending keyway formed in said outer housing, said keyway comprising an elongated top portion above an enlarged lower portion with an adjacent side portion;

an inner housing located interiorly of said outer housing;

a guide member mounted at one end of said inner housing, said guide member having at least one protrusion adapted to engage said keyway;

a spring member, said spring member having a first end abutting said outer housing, a second end of said spring member abutting said guide member;

a syringe mounted interiorly of said inner housing,

a needle mounted on one end of said syringe;

said syringe having a plunger and a plunger rod;

a finger rest member mounted over said outer housing, said finger rest member being opaque to thereby prevent visual access to said keyway;

wherein said at least one protrusion engages the adjacent side portion of said keyway prior to use of the injector;

wherein said at least one protrusion engages the top portion of said keyway if the inner housing is pushed;

wherein said at least one protrusion engages the enlarged lower portion of said keyway if the inner housing is pushed and then released;

and wherein the enlarged lower portion further comprises a somewhat horizontal wall such that when said at least one protrusion engages the enlarged lower portion, said at least one protrusion is blocked from moving out of the enlarged lower portion.