Wearable bands with embedded circuitry

A watch band configured to be coupled to a main unit of a watch, the watch band comprising:

• an elastomeric band, wherein the elastomeric band has a first portion and a second portion;
• a flexible printed circuit having serpentine portions embedded in the elastomeric band, wherein the flexible printed circuit has first electrical contacts configured to mate with second electrical contacts in the main unit of the watch;
• sensors mounted on the flexible printed circuit and configured to generate data;
• a clasp that couples the first portion of the elastomeric band to the second portion of the elastomeric band, wherein the clasp comprises interconnects that are coupled to the flexible printed circuit and carry the data;
• and
• light-emitting diodes on the flexible printed circuit that are configured to emit light through at least some of the elastomeric band material.

An electronic device, comprising:

• a strap having first and second surfaces, wherein the first surface faces a first direction and the second surface faces a second direction that is opposite the first direction;
• an electrical unit coupled to the strap;
• light-emitting diodes that emit light through the first surface in a given direction, wherein the strap comprises elastomeric polymer, wherein the light-emitting diodes are each formed in respective cavities in the elastomeric polymer, and wherein the cavities have reflective sidewalls that extend between the first and second surfaces in the given direction;
• sensors that make sensor measurements through the second surface;
• and
• a flexible printed circuit substrate coupled to the light-emitting diodes.