Guides
Getting started and frequently asked questions – all at a glance.
Installation
Lethe is an Android app that is installed via APK.
Download the APK
Download the latest APK file from the downloads page. You can start the download on your PC and then transfer the file to your device, or open the link directly on the Android device.
Allow unknown sources
By default Android blocks apps from sources other than the Play Store. Go to Settings → Security → Unknown sources and allow your browser (or file manager) to install. On Android 8+ this dialog appears automatically when you try to install.
Install the APK
Open the downloaded .apk file and tap "Install". The process takes a few seconds.
Disable battery optimization
So that Lethe reliably receives messages in the background, disable battery optimization: Settings → Battery → Battery optimization → Lethe → Don't optimize. Some manufacturers (Xiaomi, Samsung) have additional "power-saving mode" settings that also need to be disabled.
Register & get started
Open Lethe, tap "Register" and choose a Lethe number (pseudonym – not a real phone number). Share your number with friends or use the invite link from the account area.
Frequently asked questions (FAQ)
Answers to the most common questions.
Tap the "+" icon in the contact list. Enter your contact's Lethe number or scan their QR code. A contact request is sent – once the other person confirms, you can chat.
Yes. The content of every message is encrypted with the recipient's public key before it leaves the device. The server only stores encrypted blobs – the content is readable only by you and your conversation partner.
Android manufacturers (especially Xiaomi, Huawei, Samsung) aggressively try to kill background processes. Make sure that:
- Battery optimization for Lethe is disabled
- Lethe is allowed to autostart (manufacturer setting)
- No "special power-saving modes" are active
- Background activity is allowed for the app
In the app under Account → Invite → Share invite link you get a personal link. Whoever opens this link is redirected directly into the app (if installed) and your contact is automatically added to the contact request list. If Lethe is not installed, a download link appears.
Yes. Lethe supports multiple profiles. Via the profile menu (3-dot menu top right) you can switch profiles or create new ones. Each profile has its own database and settings.