Siphon



A Siphon is a device specifically designed to limit the extent of Elizabeth's powers, acting as an inhibitor to keep her under control. There are multiple functioning siphons in Columbia, found in certain locations that Booker and Elizabeth go to over the course of the game.

Function
Standard siphons are visually similar to loudspeakers, appearing as round drums typically mounted on walls and ceilings. When manually activated, they emit waves of energy that are specifically targeted at Elizabeth, appearing to cause her physical pain and discomfort. It seems that these siphons can be used to actively control Elizabeth's powers instead of merely limiting them, as Comstock uses hidden siphons built in Lady Comstock's tomb to bring an alternate version of his wife through a Tear, effectively bringing her back to life. When used passively, siphons merely limit or outright block Elizabeth's powers, keeping her under control and incapable of using Tears.

Locations

 * Monument Island: The largest siphon in Columbia is one built directly into the tower on Monument Island, serving as not only a constant limit on Elizabeth's powers while she grew up in the tower, but a seemingly permanent inhibitor with a range that extends to all of Columbia. The siphon prevents Elizabeth from accessing the godlike power she is capable of, and indeed achieves at the end of the game when the tower is destroyed. The siphon was built by Comstock when Elizabeth began to demonstrate the ability to create Tears as a child, ensuring that the tower was a permanent prison so she could no longer escape through these Tears. This siphon is ultimately destroyed by Songbird under Booker's command.
 * Memorial Gardens: A siphon is built into the walls of Lady Comstock's tomb in the Memorial Gardens, and is used by Comstock not to suppress Elizabeth's powers, but to use them to bring an alternate Lady Comstock through a Tear as the Siren against Elizabeth's will. Unlike other siphons, these appear to directly control Elizabeth's powers and cause her physical harm.
 * Comstock House: Two siphons are found in the operating theatre of Comstock House, used to completely inhibit Elizabeth's powers when performing surgery on her. These siphons are eventually deactivated by Booker, allowing Elizabeth to access her powers, open a Tear and save herself.