No carrier network, no server of our own
denntatsu doesn't go through a carrier's cell towers or our own servers. Nearby devices find each other over the air and connect directly. That's why it still works on a mountain road with no signal, or when infrastructure is down after a disaster.
Two radios, two jobs
First, Bluetooth finds nearby devices
Nearby devices say hello to each other over Bluetooth and notice one another. It uses very little power — a mechanism well suited to standing by.
Once you talk, Wi-Fi carries the voice
When a conversation starts, voice travels straight to the other device over Wi-Fi. Since it never goes through a server, it works with no cell signal at all.
Voice only reaches devices directly in range
Voice is exchanged between devices that can reach each other directly over the air. Voice itself doesn't hop across multiple devices to travel further.
SOS and safety messages travel hand-to-hand between devices
While voice and text chat only travel between directly connected devices, SOS and safety messages are passed hand-to-hand between the devices in between, gradually traveling further. If one path is blocked, a message can sometimes still arrive by hopping along a different chain of devices that are still reachable. That said, messages eventually expire as they are relayed, and delivery is never guaranteed.
If one path is blocked, a message can still get through another way
What this design can't do
- Delivery is best-effort. How far a signal reaches and whether a relay succeeds depends on nearby buildings, terrain, and how many devices are around.
- Voice and text chat only travel between devices that can reach each other directly over the air — they don't hop across multiple devices to travel further.
- SOS and safety messages are relayed between devices, but they eventually expire along the way — they are not kept indefinitely.
- Because there's no server, denntatsu isn't affected by carrier tower or server outages. On the other hand, if there's no other device nearby, there's simply no signal to connect to.
Frequently asked questions about how it works
Does it really never use a server?
That's right. denntatsu doesn't go through a carrier network or a server of ours. Nearby devices communicate directly over Bluetooth and Wi-Fi.
How far does voice reach?
Voice only reaches devices that are directly in radio range of each other — it doesn't relay across devices to travel further. Delivery is best-effort and depends on nearby buildings, terrain, and device capability.
Can SOS and safety messages reach devices that are farther away?
Yes. Devices in between pass the message hand-to-hand toward its destination. That said, messages eventually expire as they are relayed, so delivery is never guaranteed (and SOS is not a replacement for official emergency services). Regular text chat, like voice, only reaches devices you're directly connected to.
Does the SOS feature work the same way?
Yes, SOS messages are relayed between devices the same way. SOS is not a replacement for official emergency services (110/119 in Japan), and it does not guarantee delivery.
Do I need to create an account to connect?
No. You just scan a QR code to connect offline — no server registration required.
Get Started
denntatsu is available now for Android. Download it free on Google Play to get started.
