The present invention safety device is a one-piece needle assembly that has a base and a housing pivotally connected to the base. The base has a distal portion to which a needle is fitted. At the base there is formed longitudinally along its distal portion a catch mechanism that may be in the form of an anchor projection. At the back wall of the housing there is extended another catch mechanism that may be configured in the form of two clasping fingers. Also providing in the housing is an integral hook. As the housing and the base are pivoted relative to each other, and as the needle makes contact with the hook, the respective catch mechanisms at the base and the housing also make contact with each other, resulting in the coupling of the catch mechanisms and the coupling of the needle to the hook. As a result, the catch mechanisms are interlocked and the needle is fixedly retained by the hook within the housing. The catch mechanisms may also be configured as a hook and a latch in the form of a rib with an opening whereto the hook is fixedly coupled. The catch mechanisms may further be configured as respective interlockable pairs of loops and bosses. The gauge of the needle may be determined by the color of both the base and the housing, which are molded as a unitary single unit.