> ## Documentation Index > Fetch the complete documentation index at: https://docs.elata.bio/llms.txt > Use this file to discover all available pages before exploring further. # Biosignals Explained > A plain-language guide to camera heart rate, EEG headbands, and headband PPG: what each measures and what it can't tell you. A **biosignal** is a measurable signal from the body, like a heartbeat or the brain's electrical activity. Elata apps use three kinds, all from devices people already own or can buy. *** ## Camera heart rate (rPPG) **What it is.** Each heartbeat pushes blood into the skin, which changes its color very slightly. A webcam can pick up that change, too small to see with your eyes. This is called remote photoplethysmography, or rPPG. **What it can estimate.** Pulse rate, and how steady the signal is. **What affects it.** Movement, dim or flickering light, strong shadows, video compression, and low frame rates all reduce accuracy. Accuracy can also vary with skin tone and camera quality. More detail: [Camera heart rate (rPPG)](/overview/science/rppg). *** ## EEG headbands **What it is.** Electroencephalography (EEG) measures tiny electrical signals from the brain through sensors on the scalp. Consumer headbands like Muse use a few dry sensors on the forehead and behind the ears. **What it can estimate.** How strong different rhythms are, such as alpha waves, which tend to rise when you're relaxed with your eyes closed. Apps turn these into measures like "calm" or "focus." **What affects it.** Blinking, jaw clenching, movement, and poor sensor contact create signals much larger than brain activity. A few sensors can't locate activity precisely, and "calm" or "focus" scores are estimates, not direct readouts of a mental state. More detail: [EEG headbands](/overview/science/eeg). *** ## Headband PPG and heart-rate variability **What it is.** Some headbands, like Muse S, have an optical sensor that shines light into the skin and measures the reflection, the same principle as a smartwatch heart-rate sensor (photoplethysmography, or PPG). **What it can estimate.** Heart rate and **heart-rate variability (HRV)**: the small variation in time between beats, which is often linked to recovery and stress. **What affects it.** Movement, a loose fit, and short recordings. HRV in particular needs clean data over a minute or more to be meaningful. More detail: [PPG and HRV](/overview/science/ppg-and-hrv). *** ## What these signals are not Elata apps are not medical devices. They don't diagnose, treat, or monitor any medical condition. If an app shows a reading that worries you, talk to a medical professional rather than relying on the app. These measurements are useful for games, feedback, and personal exploration. They are estimates that depend on conditions, and the same person can get different readings on different days. *** ## Where processing happens All three kinds of signal are processed on your device by the [Elata SDK](/overview/elata-sdk). Raw camera frames and raw biosignals don't need to leave your device. See [Privacy and consent](/overview/privacy-and-consent). This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.