Abstract: A safety mechanism for aiding in the prevention of accidental or unintentional discharge of a needleless injection device having a power unit, a housing, a plunger disposed within the housing, a trigger assembly, and a nozzle. The safety mechanism includes a locking member which is disposed at least partially on the exterior of the housing. The locking member works in concert with the triggering assembly to the prevent movement thereof, thereby preventing activation of the power unit to eject fluids through the nozzle. The locking member also works in concert with an interlocking sleeve which prevents activation of the injector when the nozzle is removed therefrom. The safety mechanism also includes a feature for automatically returning the locking member to a locked position after activation.