Radar jammer

The Radar Jammer is an equipment item in Halo 3 that scrambles nearby players' motion sensors by creating a multitude of false dots on the enemy radar. While it can create chaos for enemies, it also has the same effect on teammates. In story mode it is rarely dropped by enemy brutes. However when deployed by the player it doesn't effect enemy AI. It is available in multiplayer in some maps.

If anyone knows they're under the effect of it, it is possible to detect the false and real enemy (Dots from the jammer almost never stop whereas enemy tend to move more carefully and stop at points, taking the red dot off your tracker) An activated jammer can also be destroyed by weapons fire.

The Radar Jammer is similar in appearance to the Power Drain and Flare, except for its reddish-brown metal color and a red glow instead of blue/yellow. Its symbol in the HUD is a dot with curved waves emitting from it.

Trivia
For a time, the Radar Jammer appeared in several maps in Halo 3 Matchmaking, but as of December 1, 2007, they have been taken out, along with the flare, perhaps due to their lack of good use.