If you're an experienced DIY-er, then you can probably mate a bronze bell with a USB-based Arduino controller in your sleep. By default the setup will ring the attached bell every 30 minutes. It's possible to modify the programming to change the timing, or even control it through a software-based tool.
From a practicality point-of-view however, the USB bronze bell isn't exactly a must-have. You can easily find a bronze bell sound effect online and use it as your software-based alarm. People nearby will also feel an uncontrollable urge to kill you after the first several rings. Still, if you can't resist, check out the instructions through the link below for a detailed step-by-step.