Devices and methods for a contact lens with an outward facing light source

1. A method comprising:

receiving, by a photodetector in a reader device, an incident signal transmitted by a body-mountable device, wherein the body-mountable device includes a transparent material, a substrate at least partially embedded in the transparent material, and a light source disposed on the substrate, wherein the transparent material has a mounting surface and a surface opposite the mounting surface, and wherein the incident signal comprises light emitted by the light source and transmitted through the surface opposite the mounting surface; and

determining, by the reader device, a message from the body-mountable device based on the incident signal received by the photodetector.

2. The method of claim 1 , wherein the light emitted by the light source and transmitted through the surface opposite the mounting surface is modulated with respect to at least one of a color, brightness, intensity, or duration.

3. The method of claim 2 , wherein the body-mountable device includes circuitry disposed on the substrate, wherein the circuitry is configured to modulate the light emitted by the light source.

4. The method of claim 3 , further comprising:

transmitting, by the reader device, data to the body-mountable device; and

transmitting, by the reader device, instructions to the body-mountable device, wherein the instructions are configured to cause the circuitry to modulate the light emitted by the light source based on the data.

5. The method of claim 4 , further comprising determining a response to the message, wherein the data and the instructions are indicative of the response.