Dispel the powers of darkness that may be in this room and protect me this night ...
A beautiful and powerful prayer from Night Prayer of the Liturgy of the Hours on special solemnities:
Lord, we [or I] beg you to visit this house [room] and banish from it all the deadly power of the enemy. May your holy angels dwell here to keep us in peace, and may your blessings be upon us always. We ask this through Christ our Lord. Amen.
A prayer written by Fr. Edward Looney, which he uses especially when he is staying in a hotel during his travels:
Almighty God, I ask you to send your angels to be with me in this place, and protect me from all assaults of the Evil One. Please forgive any wrong that has been perpetuated in this room, and grant those who offend you the grace of conversion. Dispel the powers of darkness that may be in this room and protect me this night, and those who will sleep here in the forthcoming nights. Jesus, I trust in You!
See more specific prayers at Aleteia’s section of Prayers for a Particular Need.