Blog & developer journal
Behind the scenes of building a truly private location app.
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Ask us for your data. There's almost nothing there.
Every company must hand over the data it holds on you. Fenzly's answer reads in a minute, by design, and you can verify it yourself.
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A GPS sports tracker that keeps your training to itself
Runs, rides and hikes with live speed, distance, climb and GPX export, no feed, no kudos, no public heatmap. Fenzly as a private activity tracker.
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Location sharing is not a yes/no switch
In Fenzly, every member of a circle picks their own sharing level: nothing, latest position, circle places, or everything. The dial, and why it matters.
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The timeline: a life journal, not a surveillance feed
Fenzly's heart isn't a dot on a map. It's a private journal of your days, stays and trips, computed and stored on your phone, and readable only by you.
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Olm and Matrix: where Fenzly's encryption engine comes from
Fenzly's encryption runs on Olm, born in the Matrix project. What Matrix is, how Olm was audited, how it compares to Signal, and who relies on it.
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There's no such thing as a group envelope
Sealing a message for a whole circle sounds simple. It isn't: group encryption always involves a trick, and Fenzly picked the stubborn one. Here's why.
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Car, bike or on foot? Why your phone often guesses wrong
Detecting how you travel is harder than it looks: sensors lie, speeds overlap. So Fenzly labels its guess as a guess, and lets you correct it in one tap.
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Your phone is trying to kill this app (and every other one)
iOS and Android aggressively freeze background apps, and some brands go further. What that means for a location app, and how Fenzly copes, honestly.
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How a location app can run all day without draining your battery
Fenzly doesn't keep the GPS on. It sleeps by default and wakes only when movement is worth recording. Here's the machinery, and its honest trade-offs.
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Seven questions to ask any location-sharing app
Before trusting an app with your family's movements, ask these seven questions. They apply to every location app, including ours.
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Why Fenzly costs money, and why that's good news
Running a location app costs money every day. Fenzly chose a business model that does not depend on your data, and an architecture that rules it out. Here's how it works, in full.
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What your location history reveals about you
Where you sleep, work, pray and get treated, a few days of location traces expose more than most people imagine. And anonymisation barely helps.
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How Fenzly finds your friends without seeing your address book
Finding friends usually means uploading your whole contact list to a server. Fenzly never does, here's how consented hash matching finds your friends instead.
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Swiss data sovereignty: what it actually buys you
Fenzly runs on Swiss infrastructure under Swiss law. What that genuinely protects, where the limits are, and why encryption still does the heavy lifting.
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Why turning on backup isn't optional in Fenzly
Our server holds nothing readable and your encryption keys never leave your phone. That's the point, and it's why losing your phone without a backup is final.
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How unbreakable is end-to-end encryption, really?
A myth says a powerful enough computer can crack anything. For the encryption behind Signal, WhatsApp and Fenzly, the numbers say otherwise.
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A location app that keeps working when your network doesn't
A location app often goes blank without a signal. Fenzly keeps working offline, only sharing with others is deferred until you reconnect. Here's why.
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The blind server: how a location app can't see your location
Fenzly's server stores only opaque encrypted blobs. Here's what it actually sees, what it can't, and the metadata we still can't make disappear.
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End-to-end encryption, explained without the jargon
What end-to-end encryption actually means, how Double Ratchet encryption works, and why your location stays private in Fenzly.
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Building a genuinely private location app
Why we're building Fenzly, and what a "blind server" actually means.
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