Detect Internet Explorer

ie-detect.js

function isIE() {
    var ua = window.navigator.userAgent;
    var msie = ua.indexOf('MSIE ');
    var trident = ua.indexOf('Trident/');

    return (msie > 0 || trident > 0);
}

if (isIE()) {
    document.getElementById('ie-notice').style.display = 'block';
}

Usage

1. Include the notice for IE users, it will be hidden by default

<div id="ie-notice" style="display:none;">Internet Explorer detected</div>

2. Include the script (minified version below), which will make the notice visible if a IE user is detected

<script>function isIE(){var e=window.navigator.userAgent,n=e.indexOf("MSIE "),i=e.indexOf("Trident/");return 0<n||0<i}isIE()&&(document.getElementById("ie-notice").style.display="block");</script>