When infrastructure goes down, communication itself is lost
When a disaster takes down cell towers, cellular signal itself disappears. denntatsu connects devices directly with no server or cell tower involved, using the phone you already carry. Nearby people — even complete strangers — may relay SOS and safety messages to each other.
What you can do with denntatsu
Send SOS from wherever you are
Send your GPS location and status with one tap. The disaster SOS feature is entirely free and unlimited.
Share your status on a local bulletin board
Post and read simple safety status like "I'm here" or "I'm safe" within the local ad-hoc network.
Relay works between strangers too
Even people with no prior connection can relay SOS and safety messages device-to-device if they're nearby.
How it works
- 1
Switch to disaster mode
Switch the app into disaster mode to access SOS and the safety bulletin board.
- 2
Send an SOS or a status update
Send your GPS location and status with one tap, or post to the safety bulletin board.
- 3
Nearby devices relay it onward
Other nearby devices — including strangers' devices — may relay your message to the next device.
Relay is a best-effort, device-to-device process. Messages expire as they are passed along, and delivery is never guaranteed.
What to know before you use it
- This is not a substitute for official emergency services (110/119 in Japan).
- Delivery is not guaranteed. Reach, delay, and reliability depend heavily on real-world conditions — radio conditions, device density, and distance.
- Messages are relayed from device to device, but expire as they are passed along.
- This is separate from the 30-minute limit on normal-mode calls. Disaster SOS and safety sharing are entirely free and unlimited, with no time limit.
Frequently asked questions about disaster & SOS
Is the disaster SOS feature paid?
No. Disaster SOS and safety sharing are entirely free and unlimited. Paid plans only cover normal-mode calls (30-minute limit) — disaster SOS has no time limit and no charge. That said, it is not a substitute for official emergency services (110/119), and delivery is not guaranteed.
Is this a substitute for calling official emergency services?
No. denntatsu is not a substitute for official emergency services (110/119 in Japan). Always call 110/119 first whenever that's possible. denntatsu is meant as a supplementary means for situations where those channels aren't available, connecting nearby devices directly.
Is SOS or safety status guaranteed to reach someone?
No, delivery is not guaranteed. Messages are relayed from device to device, but expire as they are passed along, and reach, delay, and reliability depend heavily on radio conditions, device density, and distance. This is also not a substitute for official emergency services.
Can I reach people I have no prior connection with?
Yes. In disaster mode, even people with no prior connection can relay SOS and safety messages device-to-device if they're nearby. Delivery is still not guaranteed, and this is not a substitute for official emergency services.
Does it work when the servers or cell towers are down?
Yes. denntatsu connects devices directly with no server involved, so nearby devices can connect directly even when cell towers or company servers are down. Delivery is still not guaranteed, and this is not a substitute for official emergency services.
Does the normal-mode 30-minute limit apply to SOS?
No. The 30-minute session limit only applies to normal-mode calls. Disaster SOS and safety sharing are entirely free and unlimited, with no time limit. Delivery is still not guaranteed, and this is not a substitute for official emergency services.
Be Ready Before You Need It
denntatsu is available now for Android. You won't know when you'll need it — download it free on Google Play today, before you lose signal.
