As you deal with the boss of each area, you'll hear the Intruder Alert theme. It's a short, but aggravating tune featuring a buzzing harmony with a snare drum accompaniment that fits the tension you'll feel as you grapple with giant cyborg, protector droid, military platoon, or whatever else you'll face at the end. The title was created by Simon Wiklund for the soundtrack album. He possibly used the Pi Pi Pi boss's dialogue as inspiration for the title.
In the liner notes of the 8-bit soundtrack, Ben Judd writes: