Watch case for the Intel Edison and Sparkfun Edison Blocks
All fastener hardware is M2.0 3mm standoffs work best between Edison + Sparkfun Block and between Sparkfun Blocks
Any push pin watch band should be compatible
Simple strap an Edison and any number of Sparkfun Edison Blocks to your wrist and go
Future open hardware heartbeat sensor Edison Block is in development, these models support that form factor
More info on Edison: https://www-ssl.intel.com/content/www/us/en/do-it-yourself/edison.html
More info on Edison Blocks: https://www.sparkfun.com/news/1589