When using the onclick handler to demonstrate, two of these activate when the space bar is pressed and one does not. Use the keyboard to tab to each one then hit the space bar.
One of these is an <a href="#"> styled to look like a button, another is a <button> and another is an <input type="submit">. If you hold down the space bar or Enter key, you can also see when the event fires — when it is first pushed down or released.
This pen is used as an example in the post Links, Buttons, Submits, and Divs, Oh Hell.