For best results, swipe your entire finger from base to tip across the home key to register your fingerprint properly. Do not bend your finger or use a fingertip during registeration as the device may not recognize your fingerprints.
Factors that will affect fingerprint recognization:
• Accessories such as key protector
• Moisture. Make sure both the screen and your fingertip are dry
• Avoid contact with metal objects such as coins, keys and necklaces which can scratch or damage the Home button that contain the fingerprint recognition sensor