It is likely due to low battery. Plug the BenjiLock into the charger and charge it until the lock is at full battery. The red LED light will appear when the lock is charging. The red LED light will disappear when the lock is fully charged.
Your finger must make contact with the silver lining around the fingerprint sensor as well as the center of the sensor in order to wake up the lock. Touching only the center of the fingerprint sensor will fail to properly wake up the lock and the red LED light will appear.