Trouble with: setAdvertising heart_rate

I'm guessing that properties is one of the flags like readable, notify, etc - but not sure which.

I'm sure that'd be in Adafruit's docs somewhere? It's not something you should really try and figure out from Puck.js's source.

And yes, 00-40 sure sounds like it should be [0x00, 0x40] to me.

That also fits with the spec I posted earlier. It'd mean:

• Heart Rate Value Format is set to UINT8. Units: beats per minute (bpm)
  
• Sensor Contact feature is not supported in the current connection
  
• Energy Expended field is not present
  
• RR-Interval values are not present.
  
  

And 0x40 is 64. So a heart rate of 64 BPM