<form method="post" action="options.php">
    <?php 
$settings = array('notifications' => sm_is_notification_enabled(), 'recurrence' => sm_get_notification_recurrence());
settings_fields('smartmockups_settings_notifications');
?>
    <table class="form-table">
        <tbody>
            <tr valign="top">
                <th scope="row" valign="top">
                    <label class="notifications" for="smartmockups_notifications"><?php 
_e('Notifications', SMART_MOCKUPS_DOMAIN);
?>
</label>
                </th>
                <td>
                    <input id="smartmockups_notifications" name="smartmockups_notifications" type="checkbox" value="1" <?php 
echo $settings['notifications'] ? 'checked' : '';
?>
 />
                    <label for="smartmockups_notifications"><?php 
_e('Check this to enable scheduled notifications', SMART_MOCKUPS_DOMAIN);
?>
</label>
                </td>
            </tr>
            <tr valign="top">
                <th scope="row" valign="top">
                    <label class="notifications" for="smartmockups_notifications_recurrence"><?php 
_e('Recurrence', SMART_MOCKUPS_DOMAIN);
?>
</label>
 /**
  * Add to Queue
  *
  * @since 1.1.0
  */
 public function add_to_queue($notification)
 {
     if (!sm_is_notification_enabled()) {
         return;
     }
     $queue = $this->get_queue();
     $queue[] = $notification;
     update_option($this->option_name, $queue);
 }