1. A system for determining whether a driver of a vehicle is drowsy, the system comprising: steering wheel sensor configured to generate a steering wheel signal; a processor configured to extract at least one feature of the steering wheel signal by identifying a pair of consecutive zero-crossings where the signal values are zero, determine a distance between the pair of consecutive zero-crossings, repeat the identifying and distance determining steps for a plurality of pairs of consecutive zero-crossings, determine a standard deviation of the distances, determine whether the driver is drowsy based on the standard deviation, and generate an alarm signal in response to determining that the driver is drowsy, wherein the processor is more likely to determine that the driver is drowsy as the standard deviation increases relative to a normal standard deviation for the driver; and, an alarm device configured to indicate that the driver is drowsy, or a safety mechanism for controlling the vehicle, wherein the alarm device or safety mechanism receives the alarm signal from said processor and is activated in response to the alarm signal.