Unlike the Silicon Labs Sensor Puck, which had a 3rd party light/UV/Pulse device (and a non-Silicon Labs Bluetooth chip on the backside), enter the Silicon Labs "Thunderboard Wear ARM".

This little guy, again a demonstration / development platform, is PACKED with goodies, and this time they are all Silicon Labs devices.

I am pointing a breadboard jumper at the ambient/UV/Pulse Detector on this guy (it's TINY):

Due to the header right next to it (and the fact I have only had it for a couple of weeks), I have yet to "wear" this, but it has the same functionality as the Puck; place your finger over that 8-pin device and you get heart rate.

It uses the Silicon Labs BGM111 Bluetooth Smart Module which has its own stack in a certified module. Also, devices like the BGM111 (and other sensors on the Thunderboard) can run in an autonomous manner where they can do "work" without waking the host processor. The components and architecture of this family of devices on the Thunderboard will yield the lowest power wearable for this application (and they have the power performance monitoring tools to prove it!).

Every wearable hacker should get one of these little gems when they hit the market later in July. The Toolchain for it is incredible, and you can write code in a simple "BASIC-like" language to control it, and then do real-time power profiling. Silicon Labs rules on this suite of wearable and small form factor monitoring goodies.