Personally, I think the analog Dieter Rams Braun AB1 alarm clock still holds the title as the most perfect travel size clock, but the Braun designers have done a commendable job of capturing the simplicity+utility of the AB1 in their updated line of digital clocks designed for travelers...
Physically speaking, Rams' philosophy of "less is more" is evident in the design of the trio of Braun Digital Collection, the smallest being the 57mm x 57mm x 19.9mm model. But while the clocks are minimalist in form factor, the amount of features far exceeds their analog precursor: reverse LCD display with backlight button, 12/24 hour modes, snooze, digital tuner for radio spectrum in the UK, Japan, United States, and the rest of Europe. Available in 3 sizes, 3 colours, at three prices of $50, $60 and $100 (Goldilocks would have approved of the options).
Not much of a world traveler? One of these clocks, analog or otherwise, would make a handy timepiece/radio for the bathroom, where I've realized most of us experience those "oh shoot...I'm late for ____" moments. Also, with a clock already in the bathroom, there's no need to risk this happening to you.
(Images: Braun Time)