Pre-filled syringe safety devices and injectors, systems, and methods of use

An injector for use with a syringe having a barrel and a needle, the injector comprising:

• a cartridge configured to support the syringe;
• a casing including first and second openings, an inner surface, an outer surface opposite the inner surface, and a track defined on the inner surface, the casing configured to support the cartridge and the syringe;
• a tube including a tube distal end, the tube slidably engaged with the cartridge and configured to extend and retract relative to the first opening of the casing, wherein, in a retracted state of the tube and with the casing supporting the cartridge and the syringe, the needle of the syringe extends beyond the tube distal end and the first opening of the casing;
• a biasing member engaged with the cartridge and the tube so as to bias the tube in an extended state of the tube;
• a ring including a protrusion, the ring engaged with the tube and the biasing member, the protrusion positioned at least partially within the track;
• and
• a plunger slider extending from a plunger configured to be positioned within the barrel of the syringe, the plunger slider comprising a portion that is positioned outside the casing when the plunger is positioned within the barrel of the syringe, wherein, when the plunger is positioned within the barrel of the syringe, movement of the portion of the plunger slider and the plunger are fixed.