Siri is Apple’s new voice-controlled personal assistant that’s built right into the iPhone 4S, and she’s always glad to help whenever you ask. You can even give Siri commands when your iPhone is locked, which means there’s a chance someone could get at your schedule and contacts, and even send messages, from the locked Home screen without ever needing to know your password. Good news: You can lock down Siri so she doesn’t help anyone else without your permission.

Getting Siri’s attention is a simple as double-tapping the Home button on your iPhone 4S, and that works on a locked iPhone by default, too. Here’s how to tell Siri too keep her ears and mouth shut when your iPhone is locked:

• Unlock your iPhone 4S and tap Settings
• Tap General, then tap Passcode Lock
• Enter your iPhone unlock code to continue, then scroll down to Siri
• Set Siri to Off. If you don’t already have a passcode lock set, the Siri option is disabled and greyed out.

You can keep Siri shut down when your Home screen is locked

Setting Siri to Off in the Passcode Lock settings doesn’t disable your iPhone’s voice control features, but instead simply locks Siri so it can’t listen or respond to spoken commands when your iPhone’s Home screen is locked. You’l still have Siri at your beck and call when your phone is unlocked, and you wont have to worry about her sharing anything you’d rather keep private should someone else get their hands on your shiny new iPhone.

Interested in learning more about the features packed into iOS 5? Then check out Ted Landau’s How-to on getting the most out of Apple’s latest mobile operating system.