Reach your whole group when there is no signal.
Buzzbelt is a group chat for trips that needs no internet, no SIM and no roaming. The phones talk to each other directly over Bluetooth, and pass messages along through the group — so your reach is everybody, not just the people standing next to you.
- No internet
- No SIM
- No accounts
- Nothing leaves the phones
01 — The problem
Thirty teenagers, a city you don't know, and no way to reach them all at once.
The group spreads out the moment you arrive. Two have gone into a shop. Four are on the far side of the square. One is somewhere behind you taking a photograph of a door. You need all thirty at the meeting point in five minutes, and you need to know when you have them.
Abroad, most of their phones have no data at all. The few that do are on a parent's roaming plan that gets switched off by day two. On a hillside there is no signal to buy at any price. A group chat that needs the internet is a group chat that works at home and stops at the border.
So it comes down to counting heads, walking the square twice, and sending somebody to fetch the two who went into the shop. That works. It also takes twenty minutes every single time, and it is the reason the day runs an hour late by the afternoon.
What doesn't help here
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The WhatsApp group. Needs data on thirty phones, in a country where thirty phones don't have it.
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Ringing them. Same problem, plus roaming charges nobody's parents agreed to.
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"Meet back here at four." Fine until the plan changes, and the plan always changes.
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Shouting. Carries about as far as your voice, in one direction, once.
02 — How it works
The phones in between do the work.
Each phone can only reach as far as its own Bluetooth — tens of metres. But a phone that receives a message passes it on to whoever it can reach, so a message crosses the group in steps, through the people standing between you.
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You send "Back to the bus."
Mia is round the corner, past a stone wall and forty metres of crowd. Your phone cannot reach hers. On its own, that message goes nowhere.
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Ben is in between.
He is close enough to you, and close enough to Mia. Neither of you arranged that — he is simply standing where he is standing.
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Ben's phone passes it on.
By itself, in a second or two. Ben taps nothing and sees nothing. Mia's phone shows your message as coming from you, not from Ben.
And when there is nobody in between, nothing goes. The message waits on your phone until there is a way through, and the app tells you that before you type rather than after you send. It never shows you a tick it has not earned.
03 — What it does
Five things, built for a leader with thirty people to move.
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Group chat
One conversation for the whole trip, and a direct message to any one person. Messages that cannot get through yet wait on the phone and go the moment there is a way.
"Nobody is in reach. What you send waits here until somebody is."
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Buzz
Rings every phone in reach at full volume and takes over the screen, even locked in a pocket. It is how you get thirty heads to look up at once. Rate-limited on purpose, so it keeps meaning something.
"12 phones will ring at full volume, right now."
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Who's reachable now
A headcount of the phones yours can actually hear, updating on its own. When it cannot tell — because you stopped looking, or the radio is off — it shows a dash. Never a confident zero.
"— of 30 reachable · not looking"
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Signed leader announcements
Your instructions arrive in a frame no member's phone can draw — full width, a blaze down the edge, a seal, all checked against your key. A signature that fails is shown as failed, never quietly downgraded to an ordinary-looking message.
"Everyone back to the bus now." — signed by you
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QR join at departure
You show a code on your screen, they point a camera at it, they are in the group with your key on their phone. Nothing about joining needs a signal — the code is read off your screen, not fetched from anywhere.
No accounts. No phone numbers. No invite links.
04 — Setup in practice
You do this once, standing at the coach door.
It is designed for the two minutes you actually have: everybody queuing, bags going in the hold, one parent still talking to you.
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Before the day — everyone installs the app
The only step that needs the internet. Put it in the kit list with the boots and the water bottle, and check it at the gate rather than on the pavement. Nothing after this point needs a signal.
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You create the group
One tap. It makes a key that stays on your phone and marks you as the leader — that key is what makes your announcements checkable later.
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You hold up the QR code
One screen, and it stays up as long as you need it. You are not passing your phone around and you are not reading a code out loud.
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They scan it as they file past
Camera up, code read, type a name, done — a couple of seconds each, in the queue they are already standing in. Their name appears on your list as they board, so you can see who has not done it yet.
That is the join, not the install — the install is the night before, and a group where half of them are still downloading at the coach door will take as long as the wifi does. It also assumes you are scanning them as they board rather than gathering everybody round afterwards, which is the whole reason the code sits on your screen instead of theirs.
05 — Honest limits
What Buzzbelt cannot do.
You are deciding this on behalf of a group of other people's children. Decide it knowing exactly where the product stops — including the one thing it must never be used for.
Not a locator, and not for emergencies.
Buzzbelt cannot tell you where anybody is. It has no location permission, no map and no way to get one. "Reachable" means two phones can hear each other — not that a person is safe, not that they are nearby, not even that they are holding their phone.
If somebody is genuinely missing, this app is not part of finding them. Call them, call the police, and do everything you would have done without it. Never let a name on a screen end a search.
Bluetooth range is short.
Tens of metres between two phones in the open, and less — often much less — through walls, through a crowd, or with the phone in a back pocket. Two floors of a hostel is frequently enough to break the link between two people standing almost above each other.
It works because the group is near each other.
Every message travels through the phones in between. A group spread along one street covers that street well, and the more of you there are, the further it reaches.
But somebody who has walked away from everybody is reachable by nobody. There is no phone in between to carry it, so there is no message and no headcount entry — exactly when you would most want one.
It costs battery.
The app keeps the radio working all day, and a phone spending the day listening for thirty others does not last as long as one that isn't. Plan for a power bank on a long day. A flat phone is out of reach in exactly the same way a distant one is.
Encrypted for your group. Readable by everyone in it.
Messages are encrypted so that phones outside your group cannot read them. Inside the group there is no privacy from each other: anyone who scanned your code can read every group message.
Treat it as a room everybody is standing in. Phones get borrowed, unlocked and handed round on a trip, so nothing should go through Buzzbelt that you would not say out loud to the whole group.
06 — Questions
Questions leaders actually ask.
Does it need internet, a SIM or roaming?
No. Once the app is installed, nothing it does touches the internet. There is no server to reach, no account to log into and no data to buy. Phones in flight mode still work, as long as Bluetooth is switched back on — which flight mode allows.
The install itself is the exception: getting the app onto a phone means downloading it from a store, so do that before you travel.
How far does it actually reach?
Between any two phones, tens of metres in the open and less indoors or in a crowd. Across the group it reaches further, because each phone passes messages on — but every extra step needs a real person standing in the gap. Thirty people along a street is a long chain. Three people in a large park is three separate islands.
What happens when a message doesn't get through?
It waits on your phone and goes as soon as there is a way through. The app says so before you type, not after you send, and it distinguishes between "passed on to nearby phones, not confirmed" and "arrived on their phone". It will not show you a confirmation it did not receive.
Does it ask for location permission?
No — and it cannot be persuaded to. The app requests Bluetooth permissions only, flagged so the phone knows they are never used to derive location. There is no location permission in it to grant, which is also why it cannot tell you where anyone is.
Who can read our messages?
Everyone in your group, and nobody outside it. Messages are encrypted for the group, so another group in the same square sees nothing. Within your own group assume everything is readable by everyone — see the honest limits above.
Does it drain the battery?
Yes, noticeably. The radio has to keep working with the app in a pocket — that is what makes a buzz reach a phone nobody is looking at. On a long day, plan for power banks the way you would plan for water.
Anyone can stop the search from inside the app to save battery. If they do, the app is loud about what it costs: nothing reaches them, and a buzz will not ring.
Do the young people need accounts?
No. No account, no email address, no phone number, no age gate to lie on. They scan your code and type the name they want the group to see. That name is the only thing anybody has to give.
Where does our data go?
Nowhere. There are no servers behind this app, so there is no copy of anything to hold, hand over or lose. Conversations live on the phones that were in the conversation, and deleting the app takes its share with it. There is no analytics and no crash reporting.
Which phones does it work on?
Android 12 and later, and iPhone. Both need Bluetooth Low Energy, which every phone of that age has. Android and iPhone talk to each other normally — a mixed group is the usual case, not a special one.
Can a member pretend to be the leader?
Not in a way that survives a look. Announcements are signed with the key made when you created the group, and the app draws them in a frame that a typed message cannot produce — full width, a blaze down the edge and a seal, none of which can be imitated with text or an emoji. A message claiming to be from you without a valid signature is shown as failed, not as an ordinary message.