Inspired by Ki-Alerts https://mods.factorio.com/mod/Ki_Alerts from Matze97, I decided to create my own, custom alerts for the game.
Because they turned out really usable, I want to share this with you.
System-Alerts has 13 custom alert message sounds and 1 generic alarm. I tried to make this as less annoing as possible, so nobody gets ear cancer. :)

Alerts:
- Enemy inbound
- Fill level is at 5%
- Fill level is at 10%
- Fill level is at 20%
- Fill level is at 30%
- Fluid is low
- Oil supply is low
- Power is low
- Resources are low
- Security breach detected
- Storage tank is almost full
- Train is stuck
- Warning
- Water supply is low

Feedback and any suggestions for more alert messages are welcome. Have fun with it!