Hi there,
You can refer how Joomla achieved this as you can see on here .../modules/mod_login/tmpl/default.php on codes below.
[gist type="php"]
<?php if (JPluginHelper::isEnabled('system', 'remember')) : ?>
<div id="form-login-remember" class="control-group checkbox">
<label for="modlgn-remember" class="control-label"><?php echo JText::_('MOD_LOGIN_REMEMBER_ME'); ?></label> <input id="modlgn-remember" type="checkbox" name="remember" class="inputbox" value="yes"/>
</div>
[/gist]