Although Flash is reaching more and more devices every day and expects to be on 50% of all mobile devices by 2012, it is always a good idea to have alternative content for older devices that can not support Flash, or users that choose to disable it.
Here are a few quick ways for web designers/developers to display alternative content for devices without Flash.
1) Embed Code
var flashSupported = document.getElementById('myContent');
// if flash is not supported then go to a HTML page
if( flashSupported.innerHTML.indexOf('embed') == -1 )
3) Flash Player Detection Kit
The Flash® Player Detection Kit helps developers implement robust player detection for a variety of deployment environments by providing a set of templates and techniques to successfully detect the version of Flash Player installed on a user’s computer, and, if needed, to then install the latest version of Flash Player. The kit also includes a detailed explanation and sample files for implementing the new, player-based Flash Player Express Install experience. http://www.adobe.com/products/flashplayer/download/detection_kit/
4) User Agent
If you have some programming knowledge you can check the User Agent sent from the browser. If you know the agents that do not have Flash support or you would like to show alternative content this is easily done.