Scams win through isolation and urgency: a "nephew" on a new number, a deadline tonight, and a request not to tell anyone. Older parents living far from their children are the easiest targets, and once a transfer leaves the account it is almost never recovered. Families want a way to be there at the one moment that matters, without watching every payment.
What exists and what is new
Closest: guardian features in some crypto wallets and lookup sites like ScamWarners. Guardians in crypto wallets are for recovering a lost key, not for checking a payment, and lookup sites only help if the victim thinks to search. New: a social second key for first-time payees in an everyday wallet, paired with an automatic scam check, so a scammer has to fool two people at once while normal payments still clear in under a minute.
The data it runs on
Payee details (number, account age, name on the account), public scam reports from community lists, and the friend the user chooses. When the user forwards it, the chat that asked for money is read for pressure language. It never needs the user's full history or balance to be shown to the co-signer.
1. The mission
Nobody loses their savings alone. Every wallet comes with a second signature held by someone who loves you, and a shared memory of every scam number ever caught, so the "don't tell anyone" scam stops working.
2. Why people can't resist it
Love made practical. Adult children worry about parents abroad. Becoming the co-signer is a concrete, one-tap way to protect them.
Pride, not shame. The parent stays in control; the app frames it as "two signatures", like a cheque in the old days, not as being supervised.
The saved counter. A running total of money kept in the family is a number people screenshot and tell their siblings about.
3. How it works for real
Wallet: phone or email login creates a passkey smart wallet (Coinbase Smart Wallet, Privy or Safe) holding USDC on Base. Gas is sponsored by a paymaster, so nobody sees crypto.
Second key: a spending policy module on the smart account: payments to addresses not on the allowlist, or above thresholds, need a second signer (the co-signer's passkey). Below the line, one signature is enough.
Scam check: when a payment pauses, a fast cheap model (Gemini Flash or DeepSeek via OpenRouter) queries public scam-report lists, account age and payee name match, and scores the forwarded chat for pressure phrases. A frontier LLM like Claude writes the 4-line plain-language summary for the co-signer.
Co-sign request: push notification to the co-signer with evidence and three buttons: Approve, Call first, Block and report. Backup co-signer after 20 minutes. Money stays in the parent's wallet the whole time.
Watch mode: a scheduled worker re-checks watched numbers every few hours and links numbers sharing a receiving account. Verdicts feed a shared registry.
Fiat rails: local on and off ramps (cards, bank transfer, mobile money) so the parent sees soles, pesos or naira, not tokens.
4. Cost per use
Scam check on a paused payment: about $0.003 with a Flash-class model plus a free list lookup. Co-signer summary with a frontier model: about $0.01. Watch-mode re-checks: about $0.02 per watched number per week. Gas on Base: under $0.01 per co-signed transfer, sponsored. A family with 15 first-time payments a month costs well under $0.40 to run.
Free: one person protected, one co-signer, scam check, block and report. Paid ($3.99 per month per family): family circle up to 6 people, backup co-signers, watch mode, weekly digest, late-night rules. Revenue also from on-ramp partner fees, and later from banks licensing the co-sign module.
5. Growth loop
Every protected person brings at least one co-signer, who installs the app to sign. Co-signers then protect their other parent, an aunt, themselves. Each blocked scam produces a share card ("Mamá almost sent $1,200 to a fake nephew") that lands in exactly the family group chats where the next user lives. Every Sunday the family runs one safe simulated scam on the protected person, and the household safety score that climbs week by week gives co-signers a reason to open the app even when nothing is wrong.
6. Risks and guardrails
Control and dignity: the co-signer never sees the balance or full history, only paused payments. Rules can be tightened by the owner alone, loosened only with both signatures.
Abusive co-signers: the owner can remove a co-signer after a 48 hour cool-down, and a support line can unlock in cases of financial abuse.
False positives: the AI only scores and explains; a human always decides. Reports to public lists happen only after a co-signer taps Block and report.
Privacy: chats are read only when forwarded or when they request money, processed then deleted. Nothing is sent to anyone as the user. General information only, not legal or financial advice.
7. MVP build order
Smart wallet with email login on Base Sepolia and a two-signer policy for non-allowlisted payees.
Co-signer invite link and push approval card with Approve and Block.
Scam check: list lookup plus a Flash-model pressure-language score and a short summary.