Using Cmd + Space as your Alfred hotkey
To set your hotkey, go to the Alfred preferences and view the General tab. Type your key combo (ctrl, alt or cmd + space/character) to set it.
1. Check it isn't in use by Spotlight
If Cmd + Space doesn't work, that hotkey may be assigned to another feature on your Mac. First, verify that it's not in use for Spotlight by opening Spotlight's System Preferences and disabling the menu keyboard shortcut under Keyboard Shortcuts > Spotlight.
2. Check it isn't used for language switching
If you use (or have previously used) multiple languages on your keyboard, it's likely to be used for language switching. Here's the procedure you will need to go through:
- Open System Preferences
- Go to Keyboard > Input Sources
- Add a second language if you only have one set (The System needs at least two languages to toggle between in order to allow the keyboard shortcut to be changed)
- Go to Keyboard > Shortcuts and choose "Spotlight" in the sidebar, ensuring that the two hotkeys are not set to Cmd + Space, then disable them by unchecking the boxes.
- In the same Keyboard > Shortcuts preferences, choose "Input sources" and check that these are also not set to Cmd + Space and their boxes are unchecked.
- Return to Keyboard > Input Sources and remove the second language if you don't wish to use it.
OS X Reserving Hotkeys:
Even if you are not actively using that key combination for Spotlight or language management, OS X may be reserving it behind the scenes. If that is the case, in the Input sources, select a second language then go to the Keyboard & Text Input section again, untick the two checkboxes relating to input source.
You can then go unselect that second language, once the key combos are changed or disabled.
In earlier versions of OS X (10.8 and earlier), the exact System Preferences panes you need to navigate to may be different; you need to ensure that you disable Input Sources and Spotlight from using or reserving the Cmd + Space combination.