warning when user forget to fill in required field

Hi
We are using a long form. When user forget to fill in required field, it will highlight that field, but if those fields are out of their screen's view, they won't see it.
It will appears that the site doesn't work when they try to hit the Submit button.

Is there anyway we can show an error message near the Submit button, or an alert message telling them that:
Required fields are not filled in. Please scroll up/down to check your form.
I have also checked this with Sign Up account in Joomla. It only highlight the fields.

Thank you very much for your help

You can use system messages plugin which will display the usual error message output in a modal popup.
http://extensions.joomla.org/extensions ... ames/25240

See you around...