Unintentional sleep and performance impairment due to extended wakefulness are often the cause of traffic and work accidents. Therefore, large-scale screening instruments assessing the ability to resist falling asleep during monotonous tasks are needed. The current widespread computer use in industrial and home settings offers the possibility to use software-based instruments as an alternative for expensive hardware interfaces to assess sleep resistance. Therefore, we propose a software-based sleep resistance task based on the procedure of the Oxford SLEep Resistance test (OSLER): the Behavioral Sleep Resistance Task (BSRT). In order to validate this instrument we submitted 36 healthy individuals to four 40-min sleep resistance challenges during a night of extended wakefulness (14, 16, 18 and 20 h). Subjective sleepiness was assessed by means of the Karolinska Sleepiness Scale and a Visual Analogue Scale for sleepiness/alertness and objective sleepiness by means of a 4-min EEG-monitored fixation task. Our results show significant correlations of BSRT hit ratio, error profiles and sleep onset latency variables with subjective sleepiness and of BSRT hit ratio and 3-6 error profiles with High-Beta Central EEG activity. Additionally, using a distribution- and scale-free sensitivity index, we found that subjective sleepiness measures are the most sensitive to the effects of sustained wakefulness, closely followed by the BSRT hit ratio and BSRT error profile 3-6.