How it works | Grandma Coin

Overview

Grandma Coin does one thing. It confirms that two specific people were on a phone call together for twenty minutes, and then moves a small, pre-purchased fraction of a stock token from a vault into both of their wallets.

The hard part is the first half. Phone carriers do not tell apps who called whom or for how long, so we cannot just read your call log. Instead, the call is placed through Grandma Coin. The app dials your relative, then dials you, and bridges the two legs. That gives us exactly the facts we need and nothing else.

ConsentRelative gets one text, taps yes, picks a stock.

CallApp bridges both phones. Timer runs while both legs are connected.

VerifyTwenty continuous minutes, live audio on both sides, both press 1 at the end.

Vault checkContract confirms it holds enough of the relative's stock to pay.

PayoutTwo equal fragments transfer on Robinhood Chain. Done.

You add a relative by phone number. They receive a single SMS from Grandma Coin with a link. Nothing to install. On the link they see who added them, what the app does, and three questions: do you agree to be called through Grandma Coin, which stock would you like, and do you want a wallet created for you.

When they tap yes, three things happen: a consent record is signed and stored, a smart-contract wallet is created for them on Robinhood Chain (they can export or transfer it later), and their number is marked as callable by you and only you. Consent can be withdrawn by replying STOP at any time. Full details on the Consent Policy page.

Why the relative picks the stock

Partly because it is charming. Mostly because it makes the relative a participant with their own preference, not a prop. A grandmother choosing Coca-Cola is exercising judgment. The app respects it.

2. The call

You tap Start call in the app. Grandma Coin dials your relative first. When they answer, it dials you. Both legs are bridged and the timer starts at the moment both are connected. Your relative sees a normal incoming call from a consistent Grandma Coin number they have saved.

The bridge is ordinary telephony. Audio passes straight through. Nothing is recorded, transcribed, or stored. The server sees four facts: when each leg connected, when each leg dropped, and a running audio-energy flag from each side that says whether anyone is talking.

// what the server knows about a call call_id: c_7f2e91 grandchild_leg: connected 14:02:11, dropped 14:24:40 relative_leg: connected 14:02:04, dropped 14:24:41 both_connected: 22m 29s live_audio: grandchild 94%, relative 96% confirmed: both pressed 1 at 14:24:38

The audio-energy flag is computed on the bridge in real time and discarded per second. It answers one question: is there a human voice on this leg right now. It cannot answer what they said.

3. Verification

A call qualifies when all of the following hold:

Both legs were connected simultaneously for at least twenty continuous minutes. A drop and redial restarts the clock.
Live audio was detected on each leg for at least seventy percent of the qualifying window. Twenty minutes of silence is not a call. Twenty minutes of one person talking is, unfortunately, a call.
Before hanging up, both people press 1 when the bridge asks. This is the human confirmation step. It takes two seconds and stops most automated abuse cold.
The grandchild's phone passes a device integrity check (App Attest on iOS, Play Integrity on Android). Emulators and rooted devices do not qualify.

If any check fails, the call still happened and nobody is penalized. It simply does not pay. The app shows which check failed so you can fix it next time.

4. The vault

The vault is a contract on Robinhood Chain that holds stock tokens. Before a payout is attempted, the contract checks that its balance of the relative's chosen stock covers two fragments. If it does not, the call is recorded as qualified but unpaid, and it pays automatically the next time that stock is topped up. Nothing is ever minted from nothing.

Every balance in the vault is a public balanceOf call anyone can run. The Vault page shows them live and links each one to the block explorer.

5. Payout

A qualified call produces one transaction: the vault transfers an equal fragment of the relative's stock to the grandchild's wallet and to the relative's wallet. The fragment size for each stock is set by the vault and shown on the rates table. The call ID is written into the transaction as a nullifier, so the same call can never pay twice.

Your relative's fragment sits in the wallet created at consent. They can leave it there forever, export the wallet to an app of their choosing, or ask you to help them sell it. Most leave it there and mention it at bridge.

Limits

Limit	Value	Why
Paid calls per relative	1 per day	Twenty minutes a day is plenty. Twice a day is a wellness check.
Relatives per grandchild	3	Keeps it a family thing, not a call center.
Grandchildren per relative	6	Big families exist. Bigger ones can write in.
Minimum call	20 min continuous	Long enough to actually talk.
Fragment size	Set per stock by vault	Sized so the vault can pay for months, not days.
Weekly cap per wallet	$15 equivalent	This is a nudge, not an income.

What stops cheating

Every incentive gets gamed. Here is what we expect and what catches it.

Attempt	What catches it
Two phones on a table, nobody talking	Live-audio threshold on both legs.
A recording playing into the phone	Press-1 confirmation at the end, plus energy patterns that do not respond to the other leg.
Adding yourself as your own relative	Relative number must differ from grandchild number and device, and cannot be a VoIP or virtual number.
Buying a stack of SIM cards	Three relatives max, six grandchildren max, weekly cap, and a device integrity check on the grandchild side.
Calling a stranger who agreed for a cut	Allowed, honestly. If two strangers talk for twenty minutes a day and split fifteen dollars a week, the app has still done its job.

Where the money comes from

Three sources, in order of appearance.

Seed treasury. We buy the initial stock tokens ourselves. This funds the first stretch of calls at the rates shown on the site.
Family top-ups. Anyone can add stock to the vault earmarked for a specific relative. A grandchild who tops up Nana's Coca-Cola is, in effect, running a savings plan that pays out only when they call her. This is the part we expect to matter most.
Sponsors. A company can sponsor its own stock in the vault. A beverage company funding fragments of itself for grandmothers who already chose it is a cheaper, kinder ad than most.

The full technical spec, contract interfaces, and integration notes are in the Docs.