Here it is, a device referred to, quite straightforwardly, as the Cranial Drilling Device with Retracting Drill Bit After Skull Penetration. The drill was designed by a team of researchers at Harvard in order to address a major shortcoming with manual drills. Such devices require neurosurgical training in order to know precisely when to stop so as to not damage underlying brain tissue. In certain instances, such as emergency rooms and the backs of ambulances, medical practitioners may require a cranial drill in order to perform procedures such as the insertion of pressure monitors, with nary a neurosurgeon to be found. The Harvard team has concocted a drill that automatically retracts back into its protective casing, as soon as it's finished drilling through the skull, using a bi-stable mechanism that is active as the drill spins.
Source: engadget.comAdded: 7 August 2012