Disclosed is a fluid injection device for a needle free syringe is provided that is spring-loadable and comprises a trigger positioned within the housing and actuated by depression of a push-button disposed opposite the dispensing end at an external actuation surface disposed transverse to the injection axis. The trigger has a trigger latch configured to release a trigger catch as heaving part of the spring-loaded piston of the device. The trigger catch is configured to urge the trigger latch in a direction transverse to the injection axis when the piston moves from the unloaded position to the loaded position. The compression spring is retained around the piston and retained within the housing by a piston head. The device further comprises a syringe adapter and a safety cap which prevents accidental triggering.