> For the complete documentation index, see [llms.txt](https://docs.senstream.com/senstream-researcher-ring-application-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.senstream.com/senstream-researcher-ring-application-user-guide/senstream-research-ring/finger-detection.md). # Finger Detection The ring uses the PPG sensor to detect the presence of a finger before enabling operation of the EDA electrodes. This is to prevent the EDA circuit being active and potentially have an external current applied and damaging the circuit. The ring will not stream EDA data without the presence of a finger in close proximity to the PPG window. The ring’s LED will flash pink indicating that streaming has been disabled since there is no finger present.

The bottom of the ring glows green when the PPG sensor is active and the ring's LED indicator is a solid pink when the EDA path is live and actively streaming data.

*** ### Participant Prep Before putting the ring on a participant and starting a session, it is recommended they wash hands, dry well, and check that hands are not too cold from outdoor activities. Cold hands can affect the quality of the electrodermal activity signal. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.senstream.com/senstream-researcher-ring-application-user-guide/senstream-research-ring/finger-detection.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.