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Glucose alerts

Vitality Tracker can tell you when your glucose goes outside a range you choose, and can warn you when a sensor stops producing believable readings.
These alerts are not a safety net, and must not be used as one.Vitality Tracker can only send a notification while its own code is running — on iPhone, that means while the app is open. It cannot override silent mode or a Focus. An alert may therefore arrive late, or never.Keep the alarms in your sensor’s own app switched on. Those are built for this; ours is for noticing patterns.

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Setting your thresholds

Menu → Settings → CGM Integration. Each direction has its own switch and its own threshold, adjustable in steps of 0.1 mmol/L. The defaults are the time-in-tight-range bounds — the same 3.9–7.8 the Live Dashboard’s own statistics count against. So an alert fires on exactly what that figure has been measuring all along.
Why low alerts are off by default. A high alert is coaching — it tells you something about a meal. A low alert looks like a safety net, and we cannot build one. Switching it on is a decision you make knowingly; being handed it silently would be a promise nobody can keep.
Allowed ranges: high 6.0–15.0, low 2.8–5.5, and they must stay at least 1.0 apart.
If you have diabetes, set your high threshold to whatever your clinician considers high for you — 10, 12, whatever it is. That does two things: it stops the app nagging about your normal, and it quietly tells the sensor-fault check what your normal looks like, so you are not warned about a broken sensor when the sensor is fine.

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When an alert fires

An excursion has to survive four gates. This is deliberately conservative — the fastest way to make somebody ignore notifications is to send too many.
1

The sensor must be past warm-up

A new sensor’s first hour is discarded. Readings from it are not trustworthy and would otherwise produce a false alert on the day you apply one.
2

The readings must be believable

If the sensor looks faulty, you get a sensor warning instead of a glucose alert. See below.
3

It must last 15 minutes

A brief crossing does not alert. Most of them come back down by themselves.
4

It must be happening now

An excursion that has already resolved is not reported. Being told at noon that you were high at half past nine teaches you to ignore the next one.

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How often you will hear about it

  • Once per episode. One alert for one excursion.
  • A new excursion always alerts, however recently the last one did. Pizza at six does not silence ice cream at nine.
  • Still going after two hours? You are told again — because whatever you expected to bring it down has not, and silence would read as that resolved.
  • A twenty-minute floor stops chatter when you hover on the boundary.

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The sensor warning

Sometimes glucose readings stop being about your body. A failing sensor can report values that look alarming and are simply wrong. When that happens you get “Check your sensor” rather than a glucose alert, and Vitality Tracker offers you the tools to deal with it rather than deciding for you. Three independent checks can raise it:
The strongest signal, and the fastest. Glucose changes at roughly 0.1–0.2 mmol/L per minute even when rising quickly.A real failing sensor in our own testing produced this:
That is about ten times faster than a body can move, in both directions. When enough recent readings jump like that, the sensor is the explanation.This check does not care what your normal is, so it works the same whether or not you have diabetes — and it catches a failure within the first hour, rather than after a day of bad data.
Requires three things together: a large share of the day below range, lows that are genuinely deep (a median under 3.2), and an unbroken run of at least an hour.All three, because a low-carb diet or a long brisk walk legitimately puts some people under 3.9 for a while. That is a diet, not a fault, and it should never be called one.
The bar depends on what you have told us:So a member with diabetes who sets their high alert to 12 is not told their sensor is broken at 13 — and if the warning does appear once, one tap settles it for good.

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When you get a sensor warning

Settings will ask you a question: were those readings correct?
  • They were correct — your ceiling is raised and you will not be asked again. This is the right answer if your glucose legitimately runs high.
  • Not right — nothing changes automatically, and you are pointed at the tool for removing the bad readings.

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Removing bad readings

If a sensor produced rubbish, that rubbish is in your averages, your time in range and your HbA1c estimate. You can take it out. On the Live Dashboard, triple-tap the cursor dot on the trace. Scroll to the other end of the bad stretch and triple-tap again. Confirm, and those readings stop counting towards everything.
The readings are marked as excluded rather than destroyed, and every figure is recalculated without them. Values you typed by hand are never touched — only readings that came from the sensor.

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What the “last check” line means

Underneath the alert rows is a small line like:
This is what the alert rule decided the last time it ran. It exists because “nothing is wrong” and “something is broken” look identical from outside. If an alert did not arrive and you expected one, this line will usually say why.

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Notification permission

The first time you switch an alert on, your phone asks whether Vitality Tracker may send notifications. If you decline, the switch stays on — your preference is remembered and starts working the moment you allow notifications in your phone’s settings. Nothing is silently discarded.

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Next

How it works

Reading density, sensor life, and what happens when the app is closed

Sharing with Apple Health

Publishing readings to your other apps