Due to the sweaty environment of fitness devices, an ON/OFF button is undesirable.

The Simblee device that I am using cannot be woken up via the smartphone app that it sends data.

That leaves wake on possible "shake" sensed by accelerometer or periodic auto wakes which would waste much power.

Am I missing other options ... suggestions much appreciated.

 

I have one of these, which I like a lot. It has buttons, a touchscreen and accelerometers. To a large degree it's "on" all the time. For instance it's a watch and it takes a heart rate reading every few minutes.

It syncs to my phone sporadically or when asked, but the bluetooth radio is likely off most of the time. The battery lasts a week or more between charges.

I think my point is that you can do whatever you want, and that it's already been done.

 

Thank you kindly for feedback.

It appears that your watch was relying on a tactile button to activate the Bluetooth connection to the smartphone.
I think that is what I must do as well.

There are many waterproof tactile buttons available, so maybe that is not such a bad option after all.

 

It appears that your watch was relying on a tactile button to activate the Bluetooth connection to the smartphone.

To be honest I'm not sure what all it does. I can initiate a sync from my phone, so the watch must have some low power way to listen for a request from the phone. I would assume sending (transmitting) the data requires far more power than listening for a trigger. I can use the watch for days without ever touching its buttons or screen. But I do have to use the touchscreen and the buttons to tell it I'm about to start a run or a swim. I can also use the touchscreen to initiate an on-demand pulse measurement, or to see summary info about the days weather, my activities, recent texts and so on.