Blog & developer journal
Behind the scenes of building a truly private location app.
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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
Free location apps are usually paid for with your data. Fenzly can't do that by design, so we charge openly instead. Here's the business model, 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
Most apps upload your entire contact list to their servers. 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
Most location apps go 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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