I used to use the beginning of clutch’s psychic warfare. The first track is some low murdering, and then it comes in hard with X-ray visions. Always woke me right up.

I also used slothrust’s “like a child hiding behind your tombstone” for a while. That also starts a little quiet and then ramps up. Never hated the song, somehow. https://slothrust.bandcamp.com/track/like-a-child-hiding-behind-your-tombstone

Now I just have one of the default alarms and I kind of hate it.