Kuiper Belt Objects(KBOs) are vast swarm of small bodies beyond the orbit of Neptune. Because they are too far from us, which means they are too faint, it's nearly impossible to detect a few km sized KBOs by direct imaging survey. Even the Hubble Space Telescope cannot detect such a small bodies.
To detect such km-sized KBOs, several survey project (like TAOS) uses stellar occultation method. Just look at the video to know what is the occultation.
When the small KBO blocks the light from background stars, any ground-base telescopes which placed inside of the shadow which KBO casts can detect brief decrease of flux of the star. By means of this, one can detect km-sized (or even m-sized) KBOs.
However it's still not easy to detect small-sized KBOs because such events last less than a second and estimated event rate is extremely rare. For more details : http://taos.asiaa.sinica.edu.tw/
