The lock screen is what you see once you wake a device up. It tells you to slide from left to right to unlock your device, followed by an optional passcode prompt. Several methods of bypassing the passcode prompt have surfaced multiple times in its lifetime.
The passcode on devices lacking a Secure Enclave can be brute-forced [Archived 2013-01-16 at the Wayback Machine] if the device is jailbroken, and the passcode is simple (four digits). It takes under 20 minutes to crack a 4 digit numeric passcode, this is the standard passcode for many users.
|4 digits||numeric (0-9)||18 minutes|
|4 digits||alphanumeric (a-z & 0-9)||19 days|
|6 digits||alphanumeric (a-z & 0-9)||196 years|
|8 digits||alphanumeric (a-z & 0-9)||755 thousand years|
|8 digits||alphanumeric, complex (a-z & special characters & 0-9)||27 million years|