In this paper, we first provide a set of situations varying in urgency that cover a range of possible transitions of control from the driver to the car and vice versa. We then present a study investigating a set of warnings designed for these situations, using all combinations of audio, tactile and visu-al modalities varying in urgency. We evaluate the warnings in a driving simulator with participants playing a game on a tablet, to simulate future driving situations. We finally pre-sent a first set of guidelines to inform drivers about auton-omous car handovers in an effective manner.