How to Detect Keypress While Not Focused

How do I detect keyPress while not focused?

Yes you can, it's called "System hooks", take a look at Global System Hooks in .NET.

Detect Key Press on Windows Without Window Focus

If you want to detect 'key press' events occurred in other processes, you should implement Global Hook. You can define a callback function for keyboard input events using SetWindowsHookEx().

Note that the callback function must be in a DLL in order to make it Global Hook.

So your myprogram.exe should link a dll implementing the hook. Then myprogram.exe would be able to detect any keyboard events on Windows.

Following is a good example with an explanation.
http://www.codeproject.com/Articles/1264/KeyBoard-Hooks

How to detect a keypress when console is not focused

As stated by @Brandon my workaround involved the SetWindowsHookEx() windows function as a key handler.

Listening for keypress when the browser isn't focused in javascript

to pause/stop a song played in background

As others have said, listening for keypress isn't possible. However, there is another way to do what you need.

If you use the Media Session API, all the standard media keys on the system will be relayed to your web application. Here's an example from the documentation:

navigator.mediaSession.setActionHandler('play', function() { /* Code excerpted. */ });
navigator.mediaSession.setActionHandler('pause', function() { /* Code excerpted. */ });

This works for Bluetooth remotes, and phone lock screens as well. Browser support is Chrome-only at the moment, but this is definitely a useful up-and-coming API that will likely see more compatibility in the near future.

Monitor keypress in tkinter without focus

I found a solution to the issue by using the system_hotkey package for python. This package allows you to assign system-wide hotkeys that work without focus on the tkinter program.

from system_hotkey import SystemHotkey
hk = SystemHotkey()
hk.register(['alt', 'q'], callback=lambda event: self.Start())
hk.register(['alt', 'w'], callback=lambda event: self.Stop())

Bear in mind that any hotkey added like this will make the registered hotkey combination inaccessible to other programs.