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One of the most popular practices amongst software developers is to leave ‘backdoors’ within the code, which essentially allow anyone with knowledge to get into the system at a much deeper level than you’d expect from an end-user. These backdoors aren’t always with a malicious intent; most of the time, they allow the OEM or programmer to get into the system for troubleshooting when other, usual modes of access have been blocked. They can be quite friendly and helpful if you know what you’re doing.
Smartphones have a good share of these as well, where they’re generally known as secret codes. Most of the time, these numeric/symbolic sequences allow you to access hidden menus, diagnostic tests, areas that could change some of the most basic parameters of your device and whatnot. These secret codes, in fact, have not been exclusive to smartphones, but have long been a part of the dumb-phones and then the feature-phones before most major OEMs joined the smartphone bandwagon. For those devices that run Android, certain codes are shared across the board, and hence, can be used on a variety of devices.
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Android codes
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What follows is a collection of some of the secret codes common to the Android platform. All of these would be entered through the phone dialer (just punch in the sequence as shown). Since most hidden menus are manufacturer specific, there’s no guarantee that they’ll work across all Android smartphones, but you can try them out nevertheless on your Samsung, HTC, Motorola, Sony and other devices. Be advised, though, that some of these can cause serious changes to your device’s configuration, so don’t play with something that you don’t fully understand.
    1. *#06# – IMEI number
    2. *#0*# – Enter the service menu on newer phones like Galaxy S III
    3. *#*#4636#*#* – Phone information, usage statistics and battery
    4. *#*#34971539#*#* – Detailed camera information
    5. *#*#273282*255*663282*#*#* – Immediate backup of all media files
    6. *#*#197328640#*#* – Enable test mode for service
    7. *#*#232339#*#* – Wireless LAN tests
    8. *#*#0842#*#* – Backlight/vibration test
    9. *#*#2664#*#* – Test the touchscreen
    10. *#*#1111#*#* – FTA software version (1234 in the same code will give PDA and firmware version)
    11. *#12580*369# – Software and hardware info
    12. *#9090# – Diagnostic configuration
    13. *#872564# – USB logging control
    14. *#9900# – System dump mode
    15. *#301279# – HSDPA/HSUPA Control Menu
    16. *#7465625# – View phone lock status
    17. *#*#7780#*#* – Reset the /data partition to factory state
    18. *2767*3855# – Format device to factory state (will delete everything on phone)
    19. ##7764726 – Hidden service menu for Motorola Droid
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Update x1: More codes!
    1. *#*#7594#*#* – Enable direct powering down of device once this code is entered
    2. *#*#273283*255*663282*#*#* – Make a quick backup of all the media files on your Android device
    3. *#*#232338#*#* – Shows Wi-Fi MAC address
    4. *#*#1472365#*#* – Perform a quick GPS test
    5. *#*#1575#*#* – For a more advanced GPS test
    6. *#*#0283#*#* – Perform a packet loopback test
    7. *#*#0*#*#* – Run an LCD display test
    8. *#*#0289#*#* – Run Audio test
    9. *#*#2663#*#* – Show device’s touch-screen version
    10. *#*#0588#*#* – Perform a proximity sensor test
    11. *#*#3264#*#* – Show RAM version
    12. *#*#232331#*#* – Run Bluetooth test
    13. *#*#232337#*# – Show device’s Bluetooth address
    14. *#*#7262626#*#* – Perform a field test
    15. *#*#8255#*#* – Monitor Google Talk service
    16. *#*#4986*2650468#*#* – Show Phone, Hardware, PDA, RF Call Date firmware info
    17. *#*#1234#*#* – Show PDA and Phone firmware info
    18. *#*#2222#*#* – Show FTA Hardware version
    19. *#*#44336#*#* – Show Build time and change list number
    20. *#*#8351#*#* – Enable voice dialling log mode, dial *#*#8350#*#* to disable it
    21. ##778 (+call) – Show EPST menu
Codes specific to HTC devices only:
    1. *#*#3424#*#* – Run HTC function test program
    2. *#*#4636#*#* – Show HTC info menu
    3. ##8626337# – Run VOCODER
    4. ##33284# – Perform field test
    5. *#*#8255#*#* – Launch Google Talk service monitor
    6. ##3424# – Run diagnostic mode
    7. ##3282# – Show EPST menu
    8. ##786# – Reverse Logistics Support
Note: Not all codes are supported in a phone. Try these codes at your own risk. 
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