A non-invasive brain-computer interface (BCI) is a headset that reads the brain's electrical signals from outside the head and turns them into measurements or commands for a computer, with no surgery and no implant. Most use EEG, electroencephalography. Small sensors called electrodes touch the scalp. They pick up the tiny voltages, a few millionths of a volt, that brain cells produce when many of them are active together.
There are two kinds of BCI. An invasive BCI places electrodes inside the skull, through surgery. It picks up clearer signals, but every user needs an operation. A non-invasive BCI sits on the head like a cap or a headband. Its signals are weaker and noisier, because they pass through the skull and the scalp. Blinks, jaw movements and the electrical wiring in the room add noise too. So much of a non-invasive BCI's work is done by the software that cleans the signal.
Here is how the signal becomes useful. A headset with 8 electrodes measures each one 250 times a second, which is 2,000 numbers every second. Software removes the noise from blinks and wiring. It then splits the signal into bands by frequency. For instance, alpha waves, at 8 to 12 cycles a second, are stronger when a person is relaxed with closed eyes. A model trained on labelled recordings turns these patterns into an output: a stress score, a sign of drowsiness, or a choice between two commands. More and more often, this model runs on the headset or the phone itself, which is called edge AI. Then the raw brain signals do not have to leave the device.
Take, for example, a research lab at an engineering college in Bengaluru that studies how attention changes during long tasks. Twenty volunteers wear headsets while they do a 40-minute task on a computer. The software records their EEG, marks the moments when their attention drops, and saves the data with the time of each reading, as time series data, for analysis.
The same headsets are used in health products. A stress headband in digital therapeutics for mental health uses EEG to train a person to relax. Research groups also use EEG to help people control a wheelchair or a cursor after paralysis, though implants are usually more reliable for that. Brain signals are sensitive personal data, which India's data protection law (DPDP Act) protects.