The siphon in BioShock Infinite

A vast machine built in the heart of Monument Island, the Siphon is a device designed to measure and absorb the vast power that lies inside of Elizabeth.

Booker encounters it during part of the Find the Girl objective in the critical story path.

As he makes his way around it, the Siphon emits a series of strange noises that sound like Elizabeth's voice humming a familiar tune, which can be seen reverberating through the air through speaker-like ports on the edges of the contraption.