Secret Codes for Android Devices

Getting IMEI:
*#06#

Information about phone, battery, and usage statistics:
*#*#4636#*#*

Access to engineering mode (for devices based on MTK processors):
*#*#3646633#*#*

Display testing:
*#*#0*#*#*

Camera information:
*#*#34971539#*#*

Reset to factory settings:
*#*#7780#*#*

Full reset and firmware reinstallation:
*2767*3855#

Firmware version information:
*#*#1234#*#*

Vibration and backlight testing:
*#*#0842#*#*

GPS module testing:
*#*#1472365#*#*

Bluetooth module testing:
*#*#232331#*#*

Wi-Fi MAC address information:
*#*#232338#*#*

Touchscreen testing:
*#*#2664#*#*

Proximity sensor testing:
*#*#0588#*#*

Delete all SMS messages:
#*5376#

Audio speaker testing:
*#*#0673#*#* or *#*#0289#*#*

Information about WLAN, GPS, and Bluetooth:
*#*#232339#*#* or *#*#526#*#* or *#*#528#*#*

Sensor testing (light sensor):
*#*#0589#*#*

USB logging:
*#*#872564#*#*

View build date information of the device:
*#*#44336#*#*

Vibration mode testing:
*#*#0842#*#*

Standalone mode testing (for Samsung):
*#9090#

Wi-Fi settings and status:
*#*#232339#*#*

G-talk status (Google Talk):
*#*#8255#*#*

HSDPA/HSUPA settings and testing:
*#301279#

Accelerometer testing:
*#*#3264#*#*

Gyroscope sensor testing:
*#*#1472365#*#*

Battery and charging check:
*#0228#

Hidden service menu (for LG devices):
3845#*device_model#

View Wi-Fi information (current SSID and IP address):
*#*#232338#*#*

Vibration and sound mode testing:
*#*#0842#*#*

Quick USB settings mode:
*#0808#

View software information (for Samsung devices):
*#1234#

SAR (Specific Absorption Rate) check:
*#07#

Secret diagnostics menu (for HTC):
##3424#

Check device serial number:
*#*#12580#369#*#*

Display dead pixel testing:
*#*#2663#*#*

FM radio testing:
*#*#526#*#*

Check factory lock status (for Samsung):
*#7465625#

Main microphone testing:
*#0283#