A tone in each ear, a few hertz apart; the pulse you hear between them is the difference. Headphones needed — through a speaker the two meet in the air and there is nothing left to hear.
Delta, theta and alpha are what these rates are called, not a claim about what they do to anyone. Not for epilepsy; not while driving.
Play 170 Hz into one ear and 176 Hz into the other and you will hear a third thing: a slow throb, six times a second, which is the difference between them. It is not in either ear. The brainstem compares what the two ears receive and the comparison is what pulses.
That is why headphones are needed. Through a speaker the two tones meet in the air before they reach you, and what you get is ordinary acoustic beating — a related effect, but not this one.
The effect works best at low carrier frequencies and small differences. Much above a thirty-hertz gap the ear stops fusing the two tones and simply hears two tones.
The names on the buttons — delta, theta, alpha, beta — are the names of brainwave frequency bands. They are used here because they are what these rates are called, not as a claim that listening to a six-hertz beat puts your brain into a six-hertz state.
That claim, usually called entrainment, has been studied for decades and the evidence remains thin and contested: small studies, inconsistent results, and effects that often disappear under proper controls. Some people find the sound settling. That is a reasonable thing to use it for, and it is all this page offers.
If anyone sells you more than that, they are selling.
The tone can follow the Sa of the raag belonging to your current prahar, so what you sit with is the same ground the station is holding. It can also be set by hand — 100, 136.1 or 210 Hz — and moved with the A = 432 switch.
A timer fades it out rather than cutting it off. It plays through a media element, so a phone treats it as playback: it keeps sounding with the screen off and names itself on the lock screen.
Not for anyone with epilepsy, and not while driving or operating anything. Keep the level low: a sustained tone at volume is a good way to tire your ears for the rest of the day.