Should he recite Aayat al-Kursi aloud or silently?
Praise be to Allaah.
It was reported in Saheeh al-Bukhaari that Abu Hurayrah (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) entrusted me with the task of looking after the Zakaat of Ramadaan. Someone came to me and started to scatter the food about, so I grabbed hold of him and said, ‘I will take you to the Messenger of Allaah (peace and blessings of Allaah be upon him)!’… He (that intruder) said: ‘When you go to your bed, recite Aayat al-Kursi, then there will stay with you a protector from Allaah, and no shaytaan (devil) will approach you until morning comes.’ The Prophet (peace and blessings of Allaah be upon him) said, ‘He spoke the truth even though he is a liar; that was a shaytaan.’”(Hadith no. 4624). It is Sunnah to recite it, and it should be recited in a voice that you can hear. And Allaah knows best.