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).
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.
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.
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.
Where processing happens
All three kinds of signal are processed on your device by the
Elata SDK. Raw camera frames and raw biosignals don’t
need to leave your device. See Privacy and consent. 
