Face recognition, iris scanning, and fingerprints are biometric authentication options found on modern iPhones and Android devices. These services can be convenient, although it is worth noting that in the US, law enforcement may be able to force you to unlock your devices as biometrics are under question when it comes to the Fifth Amendment.
If the FBI does go ahead and release its unlocking method for local law enforcement it could set a major precedent. There are hundreds of cases involving locked Apple devices, and just a fraction of those have been reported on in the wake of the San Bernardino case.
It's thought the FBI's methods of hacking into iPhones would not work to unlock the devices involved in these latest cases as they are a different model to that used by SanBernardino attacker Syed Farook's phone. 153554b96e