Flare

Overview
The flare equipment type is similar in appearance to the Radar Jammer and Power Drain and makes its debut in Halo 3. It functions in a similar manner to a flashbang grenade, blinding foes and allies alike. Its symbol in the HUD is a circle with multiple rays coming from it. This equipment type was only featured in two multilayer maps by default, including Guardian and Isolation. Both have been removed by an update.

(In reference to the Flare Equipment by Griesmer): The Flare merely creates a blinding white light rather than hurts, anyone friend or foe alike who sees it-and that's OK. "If you have a short range weapon, the flare will blind foes long enough for you to get close" says Griesemer. His favorite strategy? "See a bunch of people guarding the flag? Throw the flare down." He says "By the time the Flare's gone, their flag is too." Just take care to divert your own eyes-the Flare will blind the player who throws it, too. - ((Quote from EGM September 2007 Issue))

Disadvantages
The player cannot see the battlefield even if he/she deploys it. There is a way to counter it, but it's difficult. The flare will blind you, but your HUD, and more importantly, your reticule, is unaffected by it. If you're blinded, swing your view around until it turns red, and open fire. Many players have stated getting "lucky kills" by noticing and taking advantage of this.

Trivia

 * Although the Flare blinds you completely, it does not get rid of your motion sensor, allowing you to still know where you are. Also, if you turn away, you are able to see once again.
 * One of the best tactics for capture the flag is someone having the flare, and an ally having the Radar Jammer. That way enemies are completely unaware of your position.
 * If the player accidentally looks at an active flare, looking away will not completely get rid of the effects.
 * Using the flare in campaign will sometimes make Grunts panic and Brutes go berserk.