Recently, there has been growing interest in indoor localization, because numerous applications depend on the rapid and accurate position estimation of tagged objects. While RFID-based indoor localization is attractive, the need for a large-scale and high-density deployment of readers and reference tags is costly. Being the range-free localization, our schemes depend solely on mobile readers without reference tags or other devices, and it avoids the need of distance estimation according to RSSI or phase difference. We propose two novel algorithms, continuous scanning and category-based scheduling, for locating single and multiple tagged objects, respectively. Our primary experimental results show that the system can achieve high time efficiency and localization accuracy.