Depending on which trait is used, biometric identification systems can be quite effective at controlling access. The advantages of using biometric traits are that they are tightly bound to identity, tend to remain constant and are difficult to fool when properly implemented. And you won't leave your speech pattern on the kitchen counter at home or forget your fingerprints. Biometrics do present problems. The trick is to keep system sensitivity high enough to screen out all impostors, yet low enough that authorized users can pass through.
Some systems can be fine-tuned for accuracy or ease of use.
In high-security applications, a system can be adjusted to be so strict about matches that some authorized users may have to submit their fingerprints for scanning two or more times before they are accepted. In applications where convenience and speed is vital, recognition thresholds can be set lower, with the understanding that the system will be more vulnerable to unauthorized users. For now, fingerprints win, hands down. Not all people have scannable fingerprints. In general, though, most other biometric traits are less acceptable for system access control.