Atom Electron capture all keyboard events even when app is unfocused

For global shortcuts you can use Electron Keyboard-Shortcuts module

const {app, globalShortcut} = require('electron')

app.on('ready', () => {
  globalShortcut.register('CommandOrControl+X', () => {
    console.log('CommandOrControl+X is pressed')
  })
})

But this module support only shortcuts.
If you need any key listening/hooking you should use another module like iohook

const ioHook = require('iohook');

ioHook.on("keyup", event => {
   console.log(event); // {keychar: 'f', keycode: 19, rawcode: 15, type: 'keup'}
});

ioHook.start();

The closest thing there is to what you're looking for is global shortcuts: https://github.com/electron/electron/blob/master/docs/api/global-shortcut.md. While you don't have anything in core Electron to support capturing all keyboard events out of the box, luckily node.js is pretty extensible with native node addons.