Changing colors of cells based on other cells

I need this one spoon-fed to me. I can't seem to get it right in the conditional formatting.

I have a range of cells, B1 to B4 (with check boxes). All of them have a default value of false. If the box is checked, the value of the cell turns to true.

What conditional formatting do I place in B5 so that B5 turns to red fill if any of B1 to B4 are false?

Thanks