hide module position on mobile (xs)

Hi,

I'd like to hide module only on -xs. I've managed to do that but the code is still there although it's not visible.
I've used the responsive-option of the t3-layout and switched the module-position off on xs.

I't a custom-html-module with custom-php included. how can I physically remove module-position on xs-devices.

Do I have to implement some PHP to detect screensize?

Thanks in advance.

Mark