Now this is pretty exciting (unless you couldn't give two hoots about diagnostic reporting). Nanapho.jp has come across the Nokia Lumia 800 On-Device Diagnostic Tool, which will enable the user to perform tests and receive readouts for the accelerometer, battery, gyroscope (if supported), and more.
What's semi-interesting is the Gyroscope test reports that the Lumia 800 doesn't have support, which we're already aware of, but the tools are still an insight should you be into this kind of access. To access the tools, simply enter "##634#" on the call screen and it'll load up.
Source: nanpho.jp (translate)