OSHI for Emergencies — When the Towers Are Down

OSHI is a free, open-source, end-to-end encrypted messenger for iOS and Android that uses Bluetooth and Wi-Fi mesh networking to send messages without Internet or cellular service. OSHI does not require a phone number, email address, or account.

After an earthquake, flood, hurricane or a long power cut, cellular networks usually fail in one of two ways: the towers lose power or backhaul, or they stay up and are crushed by everyone calling at once. Either way your phone's radio still works. OSHI uses it to reach the people around you, and it carries a map that does not need a signal. This page is a practical guide to using OSHI in an emergency, including what it cannot do.

What OSHI gives you with no network

• Messages to people nearby. Over Bluetooth Low Energy at roughly 100 m in the open, relayed across up to five OSHI phones. Text, photos, voice notes and small files.
• Group chats. A family, a building, a volunteer team — one group, every member within mesh reach sees the message.
• Live location. Share where you are with your group so people can find each other.
• Offline maps with routing. Downloadable OpenStreetMap regions with search and turn-by-turn directions. Useful when the usual roads are blocked and the usual maps app shows a grey screen.
• Store-and-forward. If the person is not in range yet, the message waits on relay phones and arrives when a path appears.
• Automatic sync. The moment any phone in the chain gets a connection, queued messages deliver over the Internet too, so a message written in the dark reaches family abroad as soon as one bar returns.

Prepare before the event

1. Install OSHI on every phone in the household or team: iOS from the App Store, Android as an APK from this site (keep a copy of the APK on a phone; it can be shared to another Android by file transfer with no Internet).
2. Add each other by QR code and create the group now. No signal is needed for either step, but it is much easier at the kitchen table than in a stairwell.
3. Download the map region for your area, and the neighbouring ones.
4. Run one drill: everyone in airplane mode, send a message, share location, open the map.
5. Agree who keeps their phone charged and the app open as the household relay. A power bank is part of the kit.

During the emergency

Open OSHI and leave it in the foreground; iOS restricts background Bluetooth. Send short texts first, they travel over BLE and relay furthest. Photos go over Wi-Fi Direct and need the two phones close. Use the group for status ("we are at the school, all fine") rather than one-to-one chats, so one message informs everyone. Share live location once and let it run. If you move, the mesh moves with you: a phone carried from one shelter to another delivers everything it stored when it meets the next OSHI phone.

What OSHI cannot do, so you plan for it

• It does not call emergency services. If any cellular signal exists, a voice call to the emergency number takes priority over everything on this page.
• It does not reach across a city with no phones in between. A phone mesh is local. For kilometre links, OSHI's optional LoRa node or Meshtastic radios extend the reach; see OSHI vs Meshtastic.
• It does not relay from phones nobody installed it on. The mesh is only the people who prepared.
• Voice and video calls need an IP path; they will not run over Bluetooth alone.

Why not just SMS?

SMS is the right first try when towers are congested, because it is tiny and queues. But it dies with the tower, it reveals your number and location to the carrier, and it cannot carry a map. OSHI is the layer beneath it: no tower, no number, encrypted, and it keeps working in the building when nothing else does. OSHI is an alternative to Bridgefy, Briar, Meshtastic and bitchat for offline communication, and to Signal for private messaging. For a wider comparison see the best offline messenger page, and for shutdowns rather than disasters, the Internet shutdown survival guide.

Frequently asked questions