Is Ayatul-Kursi to be recited aloud or silently for protection from Satan before sleeping?

Reciting Ayat al-Kursi before sleep is a prescribed Sunnah, as established in Sahih al-Bukhari from the Hadith of Abu Hurayrah (may Allah be pleased with him). Its recitation protects a Muslim from Satan until morning. It is also sunnah to recite it in a voice audible to the reciter himself.