Privacy Policy

Effective date: September 27, 2026
Contact: github.com/wissam53/simtether

This document is both our Play Store privacy policy and our technical privacy posture statement. It describes what the app does with your data — which is, by design, almost nothing.

The short version

SimTether has no accounts and no analytics.
Your SMS and call data travel between your own two phones, end-to-end encrypted — over your own WiFi/hotspot by default, or (if you enable remote access) through a relay that sees only ciphertext.
We, the developers, never receive your message content or call data. With remote access enabled, our relay handles encrypted traffic and unavoidable connection metadata — described below.
The only third party involved otherwise is Google Play, if you buy the app — they handle payment, we only see whether you're entitled.

What the apps are

SimTether is two apps. SimTether Bridge runs on a cheap Android phone holding your SIM. SimTether runs on your main phone and receives SMS, call events, and call control from the bridge — end-to-end encrypted over the local network, or over the internet via a relay if you opt in.

What data the app handles — and where it goes

Data	Where it goes
SMS content	Bridge → your main phone, E2E-encrypted, over your LAN — or through the relay as ciphertext if remote access is on. Stored encrypted on both devices.
Call events	Number, state, timestamps — same encrypted path, bridge → your phone.
Contact names	Read on-device to label senders. Never transmitted to us.
Bridge telemetry	Battery, carrier, signal — sent to your paired phone so the client can show bridge status. Nowhere else.
Pairing data	Public key and token exchanged via the QR you scan. The token authenticates the encrypted session and rotates every connection.
Purchase	Handled by Google Play Billing. We see only "entitled / not entitled" — never payment details.

The encryption, specifically

Pairing is one QR scan; the bridge's public key is pinned from that moment — subsequent connections are authenticated by key, not by IP.
Sessions use Noise IK (X25519 key exchange, ChaCha20-Poly1305 transport). The WebSocket frames are ciphertext.
The app permits cleartext HTTP at the OS level because payload encryption happens inside the app — the socket itself carries only Noise ciphertext.

What we deliberately do NOT do

No analytics SDKs, no crash-reporting services, no ad networks, no trackers.
No server-side message storage. The optional relay forwards encrypted frames in memory and keeps nothing.
No account system. There is nothing to log into and nothing to leak.

Optional remote access (off by default)

If you enable remote access, your bridge phone registers with our relay server and your main phone connects through it when the phones aren't on the same network. What this means honestly:

Message content stays end-to-end encrypted. The relay forwards Noise ciphertext and cannot read it.
The relay sees connection metadata: your phones' IP addresses, connection times, data volumes, and an opaque room identifier — the minimum needed to splice the sockets.
Remote access is off unless you turn it on in the bridge app's settings, and the bridge shows a consent screen first.
You can point both phones at your own relay serverinstead of ours, in which case we see nothing at all.

The hosted relay is a best-effort service — we may change, suspend, or discontinue it at any time, or introduce a charge for hosted relay access in the future. Remote access through our relay carries no availability or pricing guarantee; the app purchase covers the app itself, not the hosted relay. If the hosted relay stops or becomes paid, local/hotspot mode and self-hosted relays keep working unchanged and free — the app itself never depends on our infrastructure to function.

Optional call audio (rooted bridge build, off by default)

The standard build forwards call control — ringing, answer, reject, DTMF — but not audio. An optional rooted bridge build can additionally capture live GSM call audio on the bridge phone and stream it to your main phone:

Audio travels bridge → your phone over the same end-to-end encrypted channel — Noise ciphertext on the LAN, and ciphertext through the relay if remote access is on. No third-party telephony provider is in the audio path.
We do not record, store, or ever possess call audio.
It requires a rooted bridge phone and ships via GitHub Releases only — the Google Play build contains no root functionality — and is off unless you enable it on the bridge.
The bridge's persistent foreground notification stays visible while the service runs — including when audio relay is active.

Permissions, honestly

The two apps split permissions by role. The bridge app asks for the sensitive set:

Permission	Used for
RECEIVE_SMS / SEND_SMS / READ_SMS	Receive incoming SMS and send replies on your SIM.
READ_PHONE_STATE / ANSWER_PHONE_CALLS / CALL_PHONE	See and control GSM calls.
NEARBY_WIFI_DEVICES	Finding the paired phone on local WiFi on Android 13+.
RECORD_AUDIO (rooted build only)	Capturing call audio for relay — asked only when you enable audio relay, never at startup.

The client app (main phone) needs none of those:

Permission	Used for
MANAGE_OWN_CALLS	Render incoming calls in the call UI.
CAMERA	Scanning the pairing QR.
NEARBY_WIFI_DEVICES	Finding the bridge on local WiFi on Android 13+ — supersedes the location permission there.
ACCESS_FINE/COARSE_LOCATION	Finding the bridge on local WiFi — Android requires location for network discovery on older versions. Never tracked or transmitted.
RECORD_AUDIO	Optional — your voice into a call, only with the rooted bridge build and only while a call is active.

Both apps:

Permission	Used for
READ_CONTACTS	Display names instead of bare numbers.
FOREGROUND_SERVICE_*	Keeping the encrypted link alive.
REQUEST_IGNORE_BATTERY_OPTIMIZATIONS	So Android doesn't kill the link — one system prompt, your choice.
POST_NOTIFICATIONS	SMS/call notifications — and on the bridge, the mandatory "bridge is on" status notice (hiding it stops the bridge).

Data retention & deletion

All data lives on your devices. Deleting a conversation in the app, or uninstalling, removes it. There is nothing to request deletion of from us — we hold nothing. (Purchase records are held by Google Play under their own policy.)

Children

The app is not directed at children under 13 and collects no data from anyone.

Changes

If this policy changes, the effective date above moves and the change lands in the public repository history — nothing happens silently.

Legal posture (KVKK/GDPR)

Your message content never reaches us — we are no data controller or processor for your SMS or calls. If you enable remote access, our relay processes the connection metadata described above (IPs, timing, volumes) as a transient transit function — not stored, not shared. The other exception is the app purchase, where Google Play is the merchant of record. For questions or requests, reach us on GitHub.