CommityHere's the uncomfortable truth about most habit and accountability apps: they don't actually know whether you did the thing. You tap "complete," and they believe you. That's fine when the only person you're accountable to is yourself and the only thing at stake is a streak. It falls apart the moment real money is on the line.
If Commity is going to charge you for missing a day, the bar is higher: it has to know you were there, and it has to be something you can't fake to yourself at 11pm. That's why the core of the app isn't a checkbox. It's a geofence.
What a geofence actually is
A geofence is just a virtual circle on the map: a center point and a radius. When you create a commitment, you pin the place that counts — your gym, your studio, the library — and that becomes the center. Step inside the circle and you're "in"; leave it and you're "out." Simple in concept; the interesting part is making it reliable.
Commity logs the minutes you actually spend inside the fence. Hit your daily goal — say 60 minutes — and the day is marked complete and your stake is safe. No button to press, nothing to remember. You just show up, and being there is the proof.
The battery problem (and how we dodge it)
The naive way to build this would be to ask the phone for a high-accuracy GPS fix every few seconds, all day. That works for exactly one afternoon, until your battery dies and you uninstall the app. Continuous high-accuracy GPS is one of the most power-hungry things a phone can do.
So Commity is deliberately lazy about it:
- It rides a low-power location stream. Instead of constantly polling, the app listens for the OS to push a new position only when you've actually moved a meaningful distance. Stand still and the radio stays quiet.
- It only spends real GPS when proximity matters. Far from your spot — at home, at work across town — no enter or exit is even possible, so the app eases off to coarser, cheaper location. It saves the precise, power-hungry fixes for when you're near the fence, where a check-in could actually happen.
- On iPhone, it sleeps until woken. iOS lets apps register a region and wake them only when you cross it. Commity stays dormant and battery-free until you approach your spot, then spins up precise tracking just long enough to do its job.
The result is an app that can track all day without being a battery-review magnet — because most of the day, it's barely doing anything.
The honesty problem: GPS wobble
Here's the subtle part most people never think about. GPS isn't a clean signal. Even when you're standing perfectly still, the reported position drifts several meters around — bouncing off buildings, fading indoors, jittering with the satellites overhead. If you treated every reading literally, a single noisy fix near the edge of your fence would register as "left the gym," then "came back," then "left" again — shredding one honest 60-minute workout into dozens of meaningless fragments.
The goal isn't to react to every GPS reading. It's to figure out the truth despite them.
Commity uses a few "anti-flap" guards to stay honest:
- Hysteresis. You count as arrived the moment you cross the fence, but you only count as left once you're clearly past it. The enter and exit lines aren't the same — that buffer absorbs edge wobble.
- An accuracy gate. A low-confidence fix (the phone tells you how accurate each reading is) is never trusted to end a visit. A fuzzy reading can't kick you out.
- Debounce. Leaving requires several consecutive confident "outside" readings, not one. A momentary glitch can't end a session you're still in the middle of.
Together these mean a single bad reading never costs you a session — but a genuine departure is still caught quickly. The system errs toward protecting the person who actually showed up.
Done the instant you hit your goal
You don't have to leave for the day to count. The moment your time inside crosses your target — the 60th minute of a 60-minute goal — the day flips to complete right there on the spot: your stake is locked safe, you get a "Goal hit!" buzz, and the evening's "you haven't shown up yet" reminders are cancelled so the app stops nagging you. Tracking for that place then goes quiet for the rest of the day. Lingering an extra hour at the gym doesn't change anything, and walking out later can't accidentally double-count the visit — once it's earned, it's settled.
Day-scoped, so midnight is clean
One more detail that matters when money's involved: each session belongs to a single day. Your minutes are banked against today's goal, and the clock doesn't quietly drag a late-night visit across midnight into tomorrow. When the day rolls over, today's tally is settled on its own terms. It keeps the accounting honest and predictable — which is the least you should expect from something that can charge you.
Why it's built this way
Every one of these decisions comes back to a single principle: the proof has to be real, and it has to favor the honest user. A check-in button fails both tests — it's fakeable, and it tempts you to cheat yourself. A geofence with careful, battery-aware, anti-flap tracking passes both. You can't tap your way to a completed day from the couch, and a flaky GPS reading can't rob you of one you earned.
That's the quiet engineering behind a simple promise: show up, and Commity will know.