To have a purpose-built heart rate monitor that sends its data telemetry out BLE using the components found on the Thunderboard will require a custom built PCB.

A viable (read: wearable) solution that could be made from off-the-shelf componentry for experimentation could be assembled that uses light-through-skin vs. the electrode method of the not-so-comfortable Polar solution I began with.

Using parts made by Adafruit such as Trinkets and other new Arduino-compatible boards they continuously design and build, along with something like the "Pulse Sensor Amped" by pulsesensor.com, I think a more comfortable "prototype" could be assembled which would include the pulse sensor, a processor, and perhaps still the nRF24L01+ transceiver for the headboard alert. But if you're going to "wear" the data processing engine anyway, then the vibrating motor could be included onboard having the same "waking impact" just as the silent alarms do on a FitBit.

Check out the Pulse Sensor Amped "kit" sold by Adafruit: https://www.adafruit.com/products/1093

And a project using it in their LEARN section: https://learn.adafruit.com/pulse-sensor-displayed-with-neopixels/the-code?view=all

I think this is where I will take the next prototype whilst working with Silicon Labs and Arrow on a version that would be the most comfortable and power efficient custom design.