A few days ago I commented on Twitter about the Fitbit's excellent battery life, and, to make the point, linked to a screenshot of the repeating OmniFocus task I created to remind me to charge the device.
Soon after publishing that tweet, Tim Roberts, Fitbit VP, pointed me to the Fitbit Low Battery Notifier, which "send[s] you an e-mail and/or text message to your phone when your Fitbit tracker's battery is low." Brilliant.
I wasn't aware that the battery information was sent to the computer OTA like the other data it records throughout the day, but Tim confirmed it was. This, together with the notifier, means that the Fitbit is off my person only when I get a text telling me it needs to be charged.
(Relatedly, the Fitbit is fantastic, and infinitely better than the WakeMate.)