Countersign

For families · works offline · free

AI can fake a voice.
It can't fake
our secret.

Scammers clone a grandchild's voice from a few seconds of video and call asking for bail money. Countersign gives your family a secret that changes every minute. A clone can sound exactly right and still not know it.

Protect my family →Try a practice call

“Grandma, it's me, Ethan…”

Ask: “What's our countersign?” The real Ethan should say:

Copper
Lantern
River

Example. Your family's words are different and change every minute.

How it works

The same idea as a bank's security code app, but spoken out loud, and built for a grandparent. No account, no server, and nothing leaves your family's phones.

  1. 01
    Scan one QR code, togetherEveryone in the family scans it once, in person, and picks their name. That's the whole setup.
  2. 02
    Everyone gets their own three wordsThey change every minute, on every phone, even with no signal.
  3. 03
    A call asks for money? Check who it really isTap “Who’s calling?”, tap their name, and ask for the words. Wrong words, or a dodge, means hang up.

Got a suspicious message?

Paste it, share it from your messages app, or drop a screenshot. An AI investigator runs real lookups (domain age, email authentication, lookalike domains, where the links go) and shows you the evidence, not just a guess.

Check a message →

Got it by email?

Just forward it

Send it to countersign@homingbox.net. The full case file comes back by email in under a minute.

Works with no signalInstalls like an app. The family words are computed on the phone, so they work in a basement or on a plane.Open protocolThe method is published with test vectors, so anyone can check it or build a compatible app.Measured honestlyWe publish how the message checker compares with a plain AI prompt, including the runs where we lost.