Mouse Button Down Question

Hello,
I was wondering if there can be a mouse button down event that isn't connected to any actor? Meaning can I just click anywhere on the screen to have an event happen? Or do I have to go through each actor and add the code?
I was wondering if there can be a mouse button down event that isn't connected to any actor? Meaning can I just click anywhere on the screen to have an event happen? Or do I have to go through each actor and add the code?