A fluid delivery device comprises a housing having a fluid reservoir. A needle is in fluid communication with the fluid reservoir in an engaged position and out of fluid communication with the fluid reservoir in armed and storage positions. A proximal end of a biasing member is coupled to the housing and a distal end of the biasing member is configured to deliver a force to the fluid reservoir. A piston member extends through the biasing member and is coupled to the distal end of the biasing member. The piston member is fixed with respect to the housing in a locked position such that the biasing member does not deliver the force to the fluid reservoir and moveable with respect to the housing in a released position such that the biasing member delivers the force to the fluid reservoir. Transitioning the needle from the storage position to the armed position transitions the piston from the locked position to the released position.
