The problem with keypad-based entry systems is simple: power. And being locked out on top of an outage may just compound the issue. Whether this secure enough for a front or back door is debatable, but as an alternative to physical-key or electronic systems from room to room inside, it seems like quite an ingenious idea indeed.
This elegant, simple, built-in mechanical solution by Jess Han lets you spin the dials to four preferred numbers, then push down the handle and open the door. Behind you, the tumblers are re-jumbled to prevent another person for simple re-opening it later on. For dark days (or nights) when the numbers might be too hard to read, a simple backlight for the white digits would be a big help as well.
The best application would seem to be storage closets to at least slow down would-be thieves, or individual bedrooms (or private areas) within a multi-unit apartment spaces and so forth. With remote code-changing systems, they would be an interesting backup system for hotels, perhaps as a failsafe for when magnetic key cards fail.