A passively activated shielding device for a catheter insertion needle. Disclosure of shielding devices according to the instant invention is provided in four embodiments. Unreleasible locking apparatus is the major differentiator in three of the devices. An accordionated or folded needle shield which markedly reduces preshielded length of one of the embodiments is the major differentiator in a fourth embodiment. Each embodiment employs a mechanical sensor which detects presence of the catheter insertion needle and its tip insertion needle within protective cover of a needle shield and passively responds to provide separation of the needle shield from an associated catheter assembly.