Inserter devices provide manual insertion of an insertion needle and cannula and subsequent automatic retraction of the insertion needle. The inserter devices include insertion guards that inhibit insertion of the insertion needle and cannula unless a compressive force applied to the device exceeds a threshold. As the user applies more compressive force, the device remains unactuated until the threshold-force is exceeded, whereupon the movement is sudden and rapid. As a result, it feels to the user that the insertion is being driven by an automatic insertion mechanism.