Smart lock maker Yale announced a new product at CES this year, designed to be fitted on doors that don't have deadbolts, which are generally required for grafting on smarts. The Assure Lever lock gets around that requirement by replacing your doorknob and lock assembly with a lever handle (hence the name) and keypad.
As they're compatible with doors that don't have deadbolts, the locks can be used on interior doors just as easily as exterior ones, in case you want to protect your home office with a key code (what are you hiding in there?). It comes in brass, nickel, and rubbed bronze finishes, with either a physical keypad or a capacitive touchscreen.
Locks are available as standalone keypads, or connected by either Z-Wave or Wi-Fi. Prices for the new units range from $149 for a non-connected number with physical keypad all the way up to $299 for one with a touchscreen and Wi-Fi. You can check them out at Yale and Amazon.