If you are wanting to use <alt>-<space> as the key for the excellent Ulauncher with Ubuntu, there are a couple of tweaks that you need to do:
1. Ensure that CompizConfig Settings Manager is installed:
apt-get install compizconfig-settings-manager
2. Start the CompizConfig Settings Manager
Go to General, General options, Key bindings and disable Window Menu which is assigned <alt>-<space> by default.
Go to the Ubuntu Unity Plugin and disable Key to show the menu bar while pressed which is assigned to <alt>.
3. Create a new desktop file for ulauncher called
with these contents:
[Desktop Entry] Name=Ulauncher Comment=Provides a convenient and fast way to launch your desktop applications Categories=GNOME;Utility; Exec=ulauncher --hide-window Icon=ulauncher Terminal=false Type=Application X-GNOME-Autostart-enabled=true X-GNOME-Autostart-Delay=5
The key part here is the autostart delay, which means that ulauncher starts a little later than other things, and the <alt>-<space> assignment works correctly.
4. Start Ulauncher and assign <alt>-<space> as the hotkey in the Ulauncher Hotkey setting.
5. Close the settings and logout and re-login and <alt>-<space> should now work to start Ulauncher, and away you go.