"Empty House" is the 16th track of the Undertale Demo OST. It plays in Toriel's Home after Toriel is killed and the protagonist attempts to sleep. It is a version of "Fallen Down" slowed down to 0.4 speed.
No one will use this anymore...Inspecting the stove after killing Toriel.
Despite not being in the Undertale Soundtrack, it still plays in the final game after falling asleep on the bed or simply turning off the lamp in the Guest Room. The song will then continue to play throughout the house regardless of the lamp or whatever room you are in in the house, making it unlike Home (Music Box).