Under iOS 8, we have two options for passcodes—either a simple, four-digit one, or a longer one that can contain both letters and numbers. For a good breakdown of how and why you might want to change yours, check out Kelly Guimont’s excellent TMO article on the subject. As she mentions, though, using a longer iOS 8 passcode isn’t the most convenient thing, as you’ll have to confirm the length of it with an extra tap when you unlock your device.
On the security of iOS 9, however, Apple says this:
The default for passcodes on your Touch ID–enabled iPhone and iPad will now be six digits instead of four. If you use Touch ID, it’s a change you’ll hardly notice. But with one million possible combinations—instead of 10,000—your passcode will be a lot tougher to crack.
Nifty! So how do you take advantage of this spankin’-new feature? Well, you’ll just visit Settings> Touch ID & Passcode (or Settings> Passcode, depending on whether your device has a fingerprint sensor). Enter your current passcode to confirm you’re authorized to make changes, and then pick “Change Passcode”:
Once you do so, you’ll of course have to put in your old passcode first, but afterward, the window will have some new options available to you for changing it.
As you can see above, touching “Passcode Options” will let you set up a new alphanumeric code (a mix of letters and numbers); a custom numeric code, which can be really long if you want the convenience of only using numbers but still need your device to be very secure; or the new choice, a six-digit code. Note that screenshot above is from my non–Touch ID iPad; the process is similar on my iPhone 6 in the current beta of iOS 9, but by default, it asks me to create a six-digit code when I go to change the passcode, and the four-digit choice is the one that’s a bit hidden:
As pointed out in the quote from Apple above, using a six-digit code is way more secure than a four-digit one anyhow, so I think everyone running iOS 9 should probably go this route.
Anyway, after you set your fancy new six-digit code, you’ll note that your lock screen looks a bit different:
I’m pretty impressed with Apple’s commitment to security on this, but I gotta confess that it’s gonna take me a while to get used to seeing six pips waiting for my passcode rather than four. I have years and years of muscle memory working against me here, folks.