"harrymc's answer is good, providing you're able/allowed to change the registry settings.
If not, you can use the Windows Calculator Accessory to convert from hexadecimal to decimal. The default mode won't do this: XP and Vista have a ""Scientific mode, whereas Windows 7, 8, 8.1 and 10 have a ""Programmer"" mode.
Select Hex base, and then type in your hexadecimal number. Then change to Dec base to see the equivalent value in decimal. That's the number you need to type into your numeric keypad while holding down the Alt key.
This might depend on the input language, and you might need to prefix a zero to the decimal value."
"On Mac OS X: open International in System Preferences, and in Input Menu select ""Unicode Hex Input"" to add this option to the input menu. Sounds obvious, but this is well hidden in the long list of languages, between Ukrainian and Vietnamese. When selected, hold down Option and type the 4 digit hex code.
Also on OS X: Calculator can be set to Programmer mode (Cmd-3), which allows for entering decimal, octal and hexadecimal codes, which are then displayed as ASCII or Unicode. However, Copy will give one the code, not the character equivalent(s). Anyone?
(For Windows, see How to enter Unicode characters in Microsoft Windows; for other input methods see Wikipedia.)
And here on Super User:
Insert Unicode characters via the keyboard? Typing strange letters ¿w/o numpad? How to type special characters in Linux?
As JMD mentioned, you can hold down Ctrl-Shift, type u1f4a9, and release in order to type U+1F4A9 in GTK+ applications (including GNOME programs, Firefox, Chromium, and LibreOffice, even under KDE). Some programs also support typing in sequence Ctrl-Shift-U, 1, f, 4, a, 9, Enter.
Unfortunately, this doesn't work in Qt applications (including KDE programs, Mathematica, and VLC). For BMP characters, there is a Unicode IBus input method. To enable, open IBus preferences and add the ""Other - unicode (m17n)"" input method (the two packages ibus-m17n and ibus-qt4 must be installed). When the cursor is in a text area, activate the input method (using the IBus toolbar or the keyboard shortcut). While active, the input method lets you type Ctrl-Shift-U followed by 4 hex digits, to input the corresponding Unicode character. This only works for BMP characters, though.
(Tested under Ubuntu.)" "Linux (including Qt/KDE applications)
As JMD mentioned, you can hold down Ctrl-Shift, type u1f4a9, and release in order to type U+1F4A9 in GTK+ applications (including GNOME programs, Firefox, Chromium, and LibreOffice, even under KDE). Some programs also support typing in sequence Ctrl-Shift-U, 1, f, 4, a, 9, Enter.
Unfortunately, this doesn't work in Qt applications (including KDE programs, Mathematica, and VLC). For BMP characters, there is a Unicode IBus input method. To enable, open IBus preferences and add the ""Other - unicode (m17n)"" input method (the two packages ibus-m17n and ibus-qt4 must be installed). When the cursor is in a text area, activate the input method (using the IBus toolbar or the keyboard shortcut). While active, the input method lets you type Ctrl-Shift-U followed by 4 hex digits, to input the corresponding Unicode character. This only works for BMP characters, though.
"It also depends where you want to use the special characters. With MS Office apps, you don't have to resort to knowing the ASCII codes for certain characters -- for example, to type a diaresis (i.e., the two dots you see above some characters in words such as naïve), in Word/Outlook/etc you can hit Ctrl + ':' (i.e., Ctrl+Shift+;) followed by 'i'.
There's a list of shortcuts available at http://word.mvpsdotorg/FAQs/General/InsertSpecChars.htm ... just scroll down to ""International Characters"".
I don't know whether any non-Office apps support similar shortcuts."
