I don't have an iPhone, but there is a security issues to be aware of:
While Siri can be a great tool, there is a security concern associated with it. By default, Siri is available all the time – even when the device is locked. This means someone could pick up your phone, even if it's locked, and say something like "Read me my last two text messages, “Send an email to xxx" or "What's my home address?"
You must disable Siri access when the device is locked with the passcode. Follow these steps to do so:
Go to Settings > General > Passcode Lock Enter your current passcode Slide Siri to the Off position Note: In the Off position, Siri will continue to function when the device is unlocked.