Wearables are a low power design challenge, often powered by a single LiPo or coin cell.
I'd estimate the simpler devices, like fitness trackers, would consume a few nA up to around 20mA.
More complex devices running an OS are going to push from nA, or likely uA, up to hundreds of mA.
So... with dynamic ranges like that - how are you measuring your system power, and calculating battery life?
Oh, and crossed-fingers isn't a good answer ;-)
Mark, measuring really lower power consumption is tricky so you need a trusty scope, here is an article on low power measurement from a The specified item was not found. engineer
Low-power measurement techniques | EDN
Its all in the probe mate!
Android Wear smartwatches have the Google Project Volta ADB batterystats functionality, so you can get detailed watch, app, and system power use statistics using that. For research measurements on custom hardware or commercial devices we also use a Monsoon Power Monitor, which uses a coulomb counter type of technique to measure power use on the device it is connected to.