Numbers don't call KeyDown

As long as the Backback is enabled, numbers do not call the KeyDown event.

Not much to replicate.
[li]Create KeyDown event in a LocalScript[/li]
[li]Put a print statement that let’s you know when a key has been pushed.[/li]

This behavior is intentional. The backpack uses the number keys in order to select a gear, therefore it only makes sense that the KeyDown event would not fire. You should be using UserInputService in situations such as this.