Secret code in Nokia Lumia 800

It is a hidden code that can enable diagnostics tool in Windows Mobile Phone for Nokia Lumia 800.
 Open up your Phone Dialer in your phone, press....
the code ##634# , it will load up the tools.

Diagnostics Tools List

• Accelerometer
• ALS
• Audio Loopback
• Bluetooth
• Camera
• Battery Status
• DTMF
• Hardware Buttons
• Headset Detection
• LCD White
• Lights
• Magnetometer
• Power Source
• Proximity
• Speaker
• Touch
• Vibra

What is the usage for these tools ?

Those tools just let you to test out is all the hardware of the phone working or not. You may use this to check your phone to make sure that all of the hardware are working correctly, like Camera, or died pixel on your LCD screen and others.