Wake Me When You Need Me

From Halopedia, the Halo Wiki

Wake Me When You Need Me is a song included in the Halo 3: Original Soundtrack. It plays during the final cutscene of Halo 3.

It starts with a wind and strings melody variation of the Gregorian chant of the Halo Theme. Later, deeper strings join in and take on the main melody, which is instantly recognized as Dust and Echoes from the ending of Halo: Combat Evolved. At 1:45, the song changes to a minor key, only to be followed by a major chord at the end.

The name of the song is derived from the final words of John-117 in Halo 3: "Wake me... when you need me."

It runs for 2:19.

Halo Original Soundtracks (Source)
Halo: CE Original Soundtrack	Opening Suite • Truth and Reconciliation Suite • Brothers in Arms • Enough Dead Heroes • Perilous Journey • A Walk in the Woods • Ambient Wonder • The Gun Pointed at the Head of the Universe • Trace Amounts • Under Cover of Night • What Once was Lost • Lament for Pvt. Jenkins • Devils... Monsters... • Covenant Dance • Alien Corridors • Rock Anthem for Saving the World • The Maw • Drumrun • On a Pale Horse • Perchance to Dream • Library Suite • The Long Run • Suite Autumn • Shadows • Dust and Echoes • Halo Theme • Siege of Madrigal
Halo 2 Original Soundtrack Volume 1	Mjolnir Mix • Blow Me Away • Peril • Ghosts of Reach • 1st Movement of The Odyssey • Heretic, Hero • Flawed Legacy • Impend • Never Surrender • Ancient Machine • 2nd Movement of The Odyssey • In Amber Clad • The Last Spartan • Orbit of Glass • 3rd Movement of The Odyssey • Heavy Price Paid • Earth City • High Charity • 4th Movement of The Odyssey • Remembrance • Connected
Halo 2 Original Soundtrack Volume 2	Cairo Suite • Mombasa Suite • Unyielding • Mausoleum Suite • Unforgotten • Delta Halo Suite • Sacred Icon Suite • Reclaimer • High Charity Suite
Halo 3 Original Soundtrack	Luck • Released • Infiltrate • Honorable Intentions • Last of the Brave • Brutes • Out of Shadow • To Kill a Demon • This is Our Land • This is the Hour • Dread Intrusion • Follow Our Brothers • Farthest Outpost • Behold a Pale Horse • Edge Closer • Three Gates • Black Tower • One Final Effort • Gravemind • No More Dead Heroes • Keep What You Steal • Halo Reborn • Greatest Journey • Tribute • Roll Call • Wake Me When You Need Me • Legend • Choose Wisely • Movement • Never Forget • Finish The Fight • LvUrFR3NZ
Halo 3: ODST Original Soundtrack	Overture • The Rookie • More Than His Share • Deference for Darkness • The Menagerie • Asphalt and Ablution • Traffic Jam • Neon Night • The Office of Naval Intelligence • Bits and Pieces • Skyline • No Stone Unturned • One Way Ride • The Light at the End • Data Hive • Special Delivery • Finale
Halo Wars Original Soundtrack	Spirit of Fire • Bad Here Day • Perspective • Money or Meteors • Flollo • Just Ad Nauseum • Unusually Quiet • Flip and Sizzle • Put the Lady Down • Six-Armed Robbing Suit • Action Figure Hands • Status Quo Show • Part of the Plan • Work Burns and Runaway Grunts • Freaked Out • Rescued Or Not • Best Guess At Best • One Problem At A Time • De Facto The Matter • Part of The Problem • Out of There Alive • Through Your Hoops • Under Your Hurdles • Insignificantia
Halo Wars Original Soundtrack DVD exclusive tracks	X-06 • Fingerprints Are Broken • Five Long Years • Nothing Ventured, Nothing Gained • Quite the Vacation Resort • We're Burning Sunshine