1) Listen to this evening's class on "Security Cameras and Motion Sensors on Shabbat," here. Follow along with the teshuvah from Yabia Omer here, and from Shevet HaLevi here.
2) Read the quote that we mentioned from R. Yisshak Yosef, regarding motion sensors here. Read Hakham Yisshak's teshuvah on security cameras here.
3) The book Orhot Shabbat (vol. 3) records that several other poskim permit motion sensors, for similar reasons to R. Vosner. See here.