Saving and retrieving value in hook_node_form_alter()
Unlike building a settings form in Drupal using system_settings_form(), you need to do more than define the form field so that it's processed. You need to define a submit handler so your custom field can be processed. In your hook_form_alter() add a submit handler:

$form['#submit'][] = 'myModule_form_node_form_submit';


Then define your submit handler to process the form value for saving. 

function myModule_form_node_form_submit($form, &amp;$form_state) {
  variable_set('node_uaid', $form_state['values']['node_uaid']);
}