Nanapho.jp has managed to find the hardware diagnostics app in the Nokia Lumia 800.
The app can be used to test whole array of different function of your phone. There are similar kind of tools for other Windows Phones, but i don’t know if the “code” is always the same.The app allows one to verify that hardware is functional, including the compass, accelerometer, speakers,Bluetooth, camera, LEDs and so forth.
Enable Diagnostic app : Dial ##634#
Here’s the list of tests you can run :
Accelerometer
ALS
Audio Loopback
Bluetooth
Camera
Battery Status
DTMF
ALS
Audio Loopback
Bluetooth
Camera
Battery Status
DTMF
Vibra
Hardware Buttons
Headset Detection
LCD White
Lights
Magnetometer
Power Source
Proximity
Speaker
Touch
Hardware Buttons
Headset Detection
LCD White
Lights
Magnetometer
Power Source
Proximity
Speaker
Touch