ZenUI Dialer & Contacts is a robust dialer app packing in a host of features. Besides letting you make calls and access contacts, the dialer also lets you block unknown and spam calls, link duplicate contacts, use speed dial, view history, run smart search, personalize the dialer theme, etc. The built-in ‘smart blocking’ tool lets you block calls from private and unknown numbers, by block list, and recognized spammers. You can also protect your private contacts with passwords. If you suspect unauthorized users are trying to hack your phone by typing in wrong passwords, you may set the front camera of your phone to function as a security camera.