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1.
A very useful machine in Half-Life 2. Created by the Combine and found along the coast, it composes of a motor and four metal beams. These beams are lifted up one at a time, then slam the sand below simultaneously. It is able to do this in rapid succession.

The vibrations caused by this frighten Antlions, and keep them at bay.

The Restrictors found along the coast are relatively small compared to the behemoths guarding the perimeter of Nova Prospekt. These are roughly twice the height of those found along the coast. When deactivated, they release a public warning system which alerts Combines in the area.

There is a two-button switch found on Restrictors, which can turn them on or off. If there are Antlions swarming all over, I suggest leaving it on.

Also called "Thumpers".
Barney saw a pack of Antlions approaching from the distance. Being the smart type, he hurried over to a nearby Restrictor, and turned it on, stopping the Antlions in their tracks.
by Comito February 12, 2008