A fluid delivery device comprising: a housing having a fluid reservoir; a needle having a storage position, an armed position, and an engaged position the needle being in fluid communication with the fluid reservoir in the engaged position and out of fluid communication with the fluid reservoir in the armed and storage positions; a cap extending over the needle in the storage position and preventing the needle from transitioning to the armed and engaged positions; a biasing member (650, 652) having a proximal end and a distal end, the proximal end of the biasing member (650, 652) being coupled to the housing and the distal end of the biasing member (650, 652) configured to deliver a force to the fluid reservoir; and a piston member extending through the biasing member (650, 652) and coupled to the distal end of the biasing member (650, 652), the piston member being fixed with respect to the housing in a locked position such that the biasing member (650, 652) 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 (650, 652) delivers the force to the fluid reservoir, characterised in that in the armed position, the needle is able to engage the fluid reservoir and transitioning the needle from the storage position to the armed position transitions the piston from the locked position to the released position, wherein the piston is releaseably coupled to the housing and wherein the cap is coupled to a pin extending through the housing and releasably retaining the piston in the storage position such that removing the cap releases the piston from the housing and transitions the needle from the storage position to the armed position. a housing having a fluid reservoir; a needle having a storage position, an armed position, and an engaged position the needle being in fluid communication with the fluid reservoir in the engaged position and out of fluid communication with the fluid reservoir in the armed and storage positions; a cap extending over the needle in the storage position and preventing the needle from transitioning to the armed and engaged positions; a biasing member (650, 652) having a proximal end and a distal end, the proximal end of the biasing member (650, 652) being coupled to the housing and the distal end of the biasing member (650, 652) configured to deliver a force to the fluid reservoir; and a piston member extending through the biasing member (650, 652) and coupled to the distal end of the biasing member (650, 652), the piston member being fixed with respect to the housing in a locked position such that the biasing member (650, 652) 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 (650, 652) delivers the force to the fluid reservoir, characterised in that in the armed position, the needle is able to engage the fluid reservoir and transitioning the needle from the storage position to the armed position transitions the piston from the locked position to the released position, wherein the piston is releaseably coupled to the housing and wherein the cap is coupled to a pin extending through the housing and releasably retaining the piston in the storage position such that removing the cap releases the piston from the housing and transitions the needle from the storage position to the armed position.