This study has investigated a practically important problem of unknown tag detection that aims to detect the existence of unknown tags in a time-and energy-efficient way. We have proposed a new SBF which is a general case of the standard BF. Based on the new filtering technique, we have further proposed the SBF-UDP. Sufficient theoretically analysis is presented to minimize the execution time as well as energy consumption of the proposed protocol. We conduct extensive simulations to evaluate the performance of our SBF-UDP, and the experimental results show that our SBF-UDP protocol considerably outperforms the previous related protocols in terms of both time efficiency and energy efficiency.