Just like us old-fashioned human beings, Apple's Siri is bright enough to know how to find information when it can't answer a question on its own.
When you ask Siri a question that it can't answer or if you tell it specifically to search the Web, the voice-based assistant uses Google as its default source. But Siri is also capable of tapping into the smarts of Bing and Yahoo, according to an article in Search Engine Land.
Noted yesterday by search engine guru Danny Sullivan, iPhone 4S users can tell Siri to use a specific search engine to answer a question. Saying "Search Bing for the weather" or "Search Yahoo for Apple news" will display results from those respective search engines.
Sullivan's finding is not quite a discovery: if you launch Siri, click on the info button, and select the Web Search option, you'll see an example of how to search a site like Bing. But it is a helpful tip, especially for iPhone 4S owners who haven't yet delved deeply into the new feature.
Users can also change Siri's default engine to Bing or Yahoo but still use Google by specifying that in their question, as in "Search Google for tips on using Siri."