Fitbit would never make a watch that accidentally shocks its owner, so I'm guessing that the next iteration of the watch will include as a feature, a built in motivator for users. If you haven't reached some percentage of your desired daily level of exercise by some predetermined time, say 3 PM, the watch will deliver a jolt to the wearer to encourage them to get with some form of activity. NOW ya lazy slacker!
If no activity is detected within a moderate length of time, say 5 minutes, another jolt is delivered. Not to worry. If the watch detects no heartbeat, it can call the EMTs.
Remember, never attribute to stupidity that which can be explained by simple corporate intent.