KN007: Measuring Phone Checks With the Screen Time API
Karui is meant to interrupt me less. I wanted to know whether that also meant picking up my iPhone less, so I read a month of my own Screen Time data through Apple’s Screen Time API.
Results
Show the data
Notifications went up, from an average of 211 a day in the first half of the month to 246 in the second. Pickups where I opened no app, picking up my iPhone, looking, and putting it down, went down from 34 a day to 23, about a third fewer.
Screen time didn’t fall: about 4.5 hours a day in both halves. I picked up my iPhone less, but stayed on it a little longer each time, about 2.1 minutes against 1.8. Most of that was X, where I watch posts about my apps: it grew from 40 minutes a day in the first week to about 68.
What the Screen Time API gives an app
An app asks for Screen Time access once, then names a date range and how to split it: by hour, day, or week. For each day it gets:
| Value | What it counts |
|---|---|
total | Pickups with no app used afterward. Apple doesn’t say whether unlocking to the Home Screen counts. |
number | Per app: pickups that went into that app. |
number | Per app: notifications from that app. |
total | Screen time, for the whole day and per app. |
first | When I first picked up my iPhone that day, and my longest session. |
It goes back about 30 days. I asked for 60 and got 31, the oldest of them empty.
The numbers stay inside a report extension. iOS runs the extension with the data and shows the view it draws inside the app, but the extension can’t send anything anywhere, not even to its own app. So an app can show these numbers but can’t keep, sync, or act on them. iOS 26.4 added DeviceActivityData.activityData(filteredBy:using:) for reading them in the app itself, but I couldn’t get that to work on my iPhone.
Building it
- The Family Controls entitlement works in development builds with automatic signing. Shipping it to the App Store needs special approval from Apple.
- With the iOS 27.2 SDK, a DeviceActivityReportScene doesn’t compile under Swift 6’s strict concurrency checking, so the test app builds in Swift 5 mode.
Caveats
- One person and four weeks, with no baseline from before Karui. Every day here was with Karui, so this is a trend while using it, not a before and after.
- I make Karui, so some of the time in it is testing.
- Days vary a lot, from 12 to 54 pickups with no app opened.
- October 24 and 25 recorded no notifications despite about 5 hours of screen time each, so they’re left out of the notification averages.
Revision History
- 2026-11-11 First published.