Mark at The Nokia Blog found a new hidden diagnostic tool that allows you to test different function on the Lumia and can be used for troubleshooting potential issues. These tests include:

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

The tool can be activated by opening the phone dialer and pressing:

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Via: The Nokia Blog