Undercurrent

Notice
what's quietly
shaping how you feel.

A private notebook for the everyday details you log: symptoms, food, sleep, the walk you almost skipped. And the patterns hiding inside them. No streaks shouting at you, no badges, no dashboards. Just what we've noticed, in soft language, when there's enough to say.

Download on iOS See how it works
iPhone On-device by default No account required
quick log · four taps
what we've
noticed lately
a streak that
doesn't nag
9:41
Tuesday, April 22
Good morning,
Lloyd.
Today 4 EVENTS
08:14
Iced oat latte
caffeine
10:32
Headache, mild
front of head
12:50
Lunch, salad bowl
homemade
15:20
Walked 2 km
outdoor
Noticed · past 30 days
Stress tags appeared before 9 of 12 low-energy events.
What it does

Four quiet jobs,
done well.

Most health apps want to be your dashboard. Undercurrent wants to be your notebook. The one you actually open. We picked four things and refused to do anything else.

01 / Capture

Log in four taps or fewer.

Symptoms, meals, meds, walks. Quick chips for what you log most. No required fields, ever. Half a thought is better than none.

02 / Keep up

Doses that log themselves.

Keep every medication in one cabinet, with its usual dose and when you last took it. Set a schedule for the ones you take regularly and they're logged for you. A daily pill box shows what's taken and what's still due.

03 / Notice

Surface what we've noticed, in soft language.

Once you've logged enough events, Insights begins surfacing co-occurrences in your own data, phrased as tends to, never causes. You decide if it's signal or noise. Findings are described, not scored.

04 / Share

Hand a clean PDF to your clinician.

One tap exports an editorial Patient pattern summary: auto-numbered observations, frequency tables, time distributions, an event log. Sized for a five-minute appointment. No portal login on the other end.

How it works

How it unfolds.

In onboarding you pick a topic: My energy, a chronic symptom, mood, sleep, or something you'll name yourself. From there, the only job is to log when something happens. The app does the noticing.

01 / Open

Open it like a notebook.

Symptoms, food, meds, walks, mood. Quick chips for what you log most. No required fields, ever. Half a thought is better than none.

02 / Notice

Let it surface what it sees.

As you log, observations appear in soft language: Poor sleep appeared before 9 of 12 low-energy mornings. Tentative on purpose. You confirm, dismiss, or keep watching.

03 / Share

Bring it to your appointment.

One tap exports an editorial PDF with observations, time distributions, and an event log. Black-and-white printable, sized for the time you actually get.

New in 2.1 · Apple Watch

Log it from
your wrist.

The entries you log most, one tap away on Apple Watch. A symptom asks how bad it is on the Digital Crown, and anything you've logged in the last day can be marked improved without reaching for your phone.

The watch's quick log: Headache, last severity 6; Omega-3, taken 4 hours ago; Morning coffee
Setting a headache's severity to 6, Significant, with minus and plus buttons around the dial
An Improving? section listing a headache logged 2 hours ago at severity 6
One tap

Your usual entries, ready.

The watch shows what you log most, with when you last took a medication and a symptom's last severity. Tapped the wrong one? Undo is right there for a few seconds.

Later that day

Mark it improved.

A symptom stays under Improving? for a day. Turn the crown to where it is now, and the time it eased lands on your timeline.

From the watch face

Start with the complication.

Add the Log complication to your watch face to open quick log in one tap. If your iPhone is out of range, logs wait on the watch until it's back.

New in 2.0 · Readings

Your numbers,
beside your days.

Glucose, heart rate, blood pressure, and weight now sit on the same timeline as everything you log. Log them by hand, or import them from Apple Health with Pro, and see how a reading moved after a meal, a walk, or a bad night.

70 180 06:00 12:00 18:00 Oatmeal Salad Pasta
Blood glucose · one day · in-range band 70–180 mg/dL
Import or log

Bring readings in.

Log a reading by hand in a couple of taps, or say it in chat: glucose 142 after lunch. With Pro, readings from Apple Health come in on their own, including a CGM's every five minutes.

See it together

Read the day at a glance.

Each day charts its readings with your events marked along the same axis, the normal range you set shaded, and exact values under your finger.

Notice (Pro)

Find what moves the numbers.

Insights compares readings after different meals and activities, before symptoms, and on out-of-range days. The clinician report gets a short summary, CGM time in range included.

Insights

What we look for,
once you've logged a while.

The Insights page is a single editorial column, hairline-divided, numbered i, ii, iii. Each observation leads with a soft-language statement, then the chart. None claim a cause. Here's a sample of what it surfaces.

i · Pre-window pattern
What shows up before symptoms.
Stress appears in the hours before symptom events — in 14 of 22 instances.
% OF DAYS WITH A SYMPTOM
With stress
64%
Without
22%
ii · Time-of-day cluster
When symptoms tend to gather.
Symptoms cluster between 2PM and 4PM.
12 AM6 AMNOON6 PM12 AM
iii · Recurring sequence
A familiar arc, repeated.
A familiar arc: caffeine → headache → rest.
9× SEEN WK 1 · WK 12
iv · Long-term (Pro)
The shape of your year.
Symptoms peak in March — across 2 years of logs.
v · Interventions (Pro)
When something helps.
Severity averaged 7.2 → 3.4 across rest episodes.
12 episodes · when taken
AVG ONSET
7.2
→
AVG DURATION
4.2 h
AVG RESOLVED
3.4
vi · Environment (Pro)
Weather as a factor.
Low pressure tracks with a +60% rise in symptom-day rate.
SYMPTOM SHARE OF EVENTS
When pressure was low
78%
Across all events
39%
8/12 FLAGGED · 18/52 OVERALL
Why we built it
"When our daughter started getting headaches, the doctor kept asking if we'd noticed any patterns, and we'd just shrug. We didn't have anywhere to keep track of the everyday details. So I built one."
L
Lloyd
Maker of Undercurrent
Research

Built on published research.

The approach behind Undercurrent rests on three ideas, all backed by published research: that logging small things changes how you think about them, that smartphone diaries can identify real triggers, and that a shared summary helps the conversation with a clinician.

Note i

Self-monitoring drives behaviour change.

A review of 85 studies found self-monitoring and feedback to be the most effective techniques in digital health interventions for chronic conditions.

Samdal et al., 2020 · Health Psychology Review Annals of Behavioral Medicine, 2023
Note ii

Smartphone diaries identify real triggers.

Clinical studies have confirmed smartphone diaries as an effective tool for trigger assessment, with daily tracking predicting symptom risk within 24 hours.

Park et al., 2016 · PLOS One Information-Theoretic Trigger Surprisal · PMC, 2025
Note iii

Shared data improves care plans.

Visual diary summaries help patients and providers focus on actionable plans rather than vague recollections during short appointments.

Chung et al., 2019 · PMC
Pricing

Honest pricing for an
app you'll actually keep.

Free

The notebook.

$0forever
  • ✓Unlimited logging of symptoms, food, meds, actions, and observations
  • ✓Medicine cabinet, dose schedules, and a daily pill box
  • ✓Log glucose, heart rate, blood pressure, and weight, charted by day
  • ✓Today, Timeline, and Calendar views
  • ✓AI chat assistant for plain-language logging
  • ✓Basic Insights: pre-window, time-of-day, day-of-week, sequences
  • ✓Local-only data, stays on your device
Download on iOS
Undercurrent Pro

Deeper patterns, on-device.

$19.99paid once
  • ✓Weather, pressure & humidity correlations
  • ✓Long-term cycles, seasonality, intervention effectiveness
  • ✓Editorial PDF report for your clinician, with auto-numbered observations and an event log
  • ✓Track multiple people, with separate threads for each
  • ✓Readings from Apple Health, including CGM glucose, analysed against your events
  • ✓Apple Health sync & iCloud backup
Download on iOS

No subscription · No recurring charges · Keep it forever

Common questions

Honest answers,
where they fit.

Where does my data live?+
On your device. The patterns engine runs on-device too. Nothing is sent to a server to be analysed. With Pro, optional iCloud backup is protected by Apple's built-in encryption; we hold no keys, see no entries, and run no analytics on your content.
How is this different from a notes app?+
A notes app stores. Undercurrent notices. Structured tags, time-windowed co-occurrences, the soft-language observations: that's the bit a notes app can't do. We owe a real debt to notes apps, though; the tone is borrowed.
What does the clinician PDF look like?+
An editorial Patient pattern summary: counts and streaks, top observations with frequency and signal, time-of-day and day-of-week distributions, an event log. Black-and-white printable, sized for a five-minute appointment. No login required on the other end.
Does it work with my CGM?+
If your CGM's app writes glucose to Apple Health (Dexcom's does), Undercurrent Pro imports those readings automatically, every five minutes of them, and keeps them on your device. You can also log fingerstick readings by hand on the free plan.
Is this medical advice?+
No. Undercurrent describes statistical co-occurrences in your self-logged data. It doesn't diagnose, treat, or replace a clinician. The phrasing (tends to, often) is deliberate. Confidence belongs to the person reading the report. Not a medical device.
What if I stop logging for a while?+
Nothing happens. No streak shame, no badges revoked, no "we miss you" emails. The app waits. When you come back, it picks up where you left off and gently asks if anything's changed.
Is Pro a subscription?+
No. Pro is $19.99, paid once. No recurring charges, no annual renewal. Pay it once and keep everything forever. The free tier gets unlimited logging and basic Insights without ever asking you to upgrade.
Why no Android yet?+
Honestly: a small team, and the on-device privacy story is easier to ship correctly on one platform first. Android is on the roadmap. We'll say more when it's real, not before.
Begin

Notice what's
already there.

Download on iOS
All data stays on your device · No account · No card