Red Alert is, as implied by the name, the theme used for Alert Mode for the original Metal Gear game for the MSX2. Befitting it being used during Alert Mode, it has an alarm klaxion playing in the background at the start, and then has a fast-paced beat to the music afterward.
The song has a brief cameo during Act 3 of Metal Gear Solid 4: Guns of the Patriots, where it can be heard inside one of the buildings of Midtown. According to the Integral Podcast commentary, the song's cameo alongside that of Theme of Tara was meant to imply the building occupant was playing Metal Gear.