At last, a dead simple way for web site publishers to detect visitors on mobile web sites! MobileESP is free, open source and lightweight. MobileESP has a simple API for detecting mobile devices. The API returns the simple Boolean result of TRUE if the device is the specified type, or FALSE if it isn’t. For example, want to know if your visitor is on an iPhone, Android or Windows Phone device? Simply use the method DetectTierIphone(). It’s that easy.