A sleepiness level detection device detects a heartbeat signal when a time equal to or longer than T1 and equal to or shorter than T2 has elapsed since the start of driving. The heartbeat signal is subjected to FFT processing to obtain a spectrum signal. By use of a peak frequency of the spectrum signal,...http://www.google.com/patents/US7206631?utm_source=gb-gplus-sharePatent US7206631 - Sleepiness level detection device
