A death watch is the latest and most Gothic iteration of wearable computing. It's called Tikker.
Tikker is a wrist watch that counts down your life from years to seconds, and motivates you to make the right choices. Tikker will be there to remind you to make most of your life...
How does it work?
The wearer simply fills out a questionnaire, deducts his/her current age from the results, and TIKKER is ready to start the countdown.
Naturally CNN has a story on this. CNN, always keen on Gothic and cybergothic stories.
This little memento mori also has a nice slogan:
(thanks to Todd Bryant)