At many security checkpoints where biometrics are used, only one protocol is employed, such as a fingerprint reader, a hand-scanner, or facial recognition. Other checkpoints use several biometric checkpoint protocols in tandem to add a layer of security. 
Complete¯an internet search for vendors of biometric products. Find one vendor with a product designed to examine several characteristics [i.e., facial recognition, hand scanner (incorporates hand pattern, fingerprint reader), retina scan, and signature recognition]. 
Discuss¯the vendor you selected along with answers to the following questions: 

Which characteristics would be more acceptable to users? 
Which would be preferred by security administrators?