To install and use the Apple Watch app, yes — the iPhone app is required as a companion, the same as most watch apps. Once installed, though, you do everything — setup, starting a set, reading the pace — from your wrist (and you'll need to grant Health access on your watch too; see below). The iPhone app can also be opened on its own to run a simplified pacing session (no Health recording) directly on your phone, with no watch involved — see the iPhone Instructions.
Any Apple Watch running watchOS 10 or later. On Series 5 and later with Always On Display enabled, the pace display stays dimly visible even when your wrist is down. Series 4 doesn't support Always On Display, so its screen sleeps normally when not actively raised or touched — pacing still works the same otherwise. If your watch supports it, we recommend turning on Always On Display before using LapPacer.
It depends which app you're using — see Purpose for a quick overview of the difference, then the iPhone Instructions or Watch Instructions for the full explanation with examples.
Its pacing display works by comparing your actual distance — detected automatically through a real Health workout session — against your target pace, so it can't function at all without Health access. If you decline, you'll see a "Health Access Needed" screen instead of Setup, with a button to try again and instructions for enabling it manually on your iPhone (Health app → Sharing → Apps → LapPacer, or Settings → Privacy & Security → Health → LapPacer). The iPhone app's own pacing session has no such requirement — see Purpose for how each app's display works.
No. LapPacer never looks at your past data — not your previous workouts, not yesterday's heart rate, nothing. The app runs no Health queries of any kind. The single figure it reads back is your average heart rate for the set you just swam, and that comes from the live workout session itself, not from a search through your records.
So why does iOS warn you about it? Because Health permissions are granted per data type, with no way to limit them to a period of time or to one app's own workouts. "Heart Rate" is the smallest thing you can grant, and granting it covers everything ever recorded. iOS is describing what the permission technically allows, not what LapPacer does with it.
LapPacer asks for read access for one reason: watchOS will not record heart rate, calories, or water temperature into your workout unless the app holds read permission for them. It's a platform requirement for writing that data, not a request to browse your history.
You can decline it. Read access is optional — pacing works exactly the same without it, because it's driven by length-completion events rather than sensor samples. Your swim is still saved, just without heart-rate and calorie detail, and the finished screen shows “—” for average heart rate. Only permission to save workouts is genuinely required.
LapPacer doesn't use GPS. It does start a real Apple Health workout session for each set, the same as the native Workout app would for a pool swim — which means watchOS automatically records heart rate, calories, and water temperature into that workout alongside the distance and stroke count LapPacer calculates, and Apple's Fitness app can show Auto Sets and Splits for it. Recording those requires LapPacer to hold read permission for them, but the only one it reads back for its own use is your average heart rate, shown when a set finishes; its pacing display is computed separately — see the Privacy Policy for details.
Yes. Starting a set begins a real Swimming workout session, saved to Health under the name “LapPacer” (not the generic “Pool Swim”) once the set ends or is stopped early.
Not on the watch — access is required there now, since the watch app's pacing display depends on a live Health workout session to detect each length. If you'd rather not grant it, use the iPhone app instead: its own pacing session has no Health dependency at all, just a simpler climbing-number display with no workout recorded. Since you're reading it off a phone screen instead of your wrist, place the phone somewhere you can see it as you make each turn, so you can compare the length you're starting (or just finished) against the number displayed.
Every set automatically locks your watch's touchscreen against accidental taps from water once it begins, the same as the native Workout app — there's no Setup toggle for this, it's always on. To unlock it, press and hold the Digital Crown until the display says Unlocked — this also ejects water from the speaker, and immediately stops your current set (see below).
Try it once on dry land before you count on it. Water Lock is handled by watchOS itself and behaves a little differently across watch models and watchOS versions, so run a short set out of the water, check the screen locks, then press and hold the Digital Crown to confirm it unlocks and ends the set. See the Watch Instructions for the full walkthrough.
It stops your current set. Disabling Water Lock always stops the set immediately, so a mid-swim press-and-hold on the crown should be avoided unless you actually mean to end it. Nothing is lost if it happens by accident, though — you'll see the usual summary for the lengths you'd completed up to that point, and the workout is saved to Health as normal.
Press and hold the Digital Crown to disable Water Lock — this immediately stops the current set. Water Lock keeps the touchscreen locked against water for the whole set, so there's no on-screen way to stop one directly; disabling Water Lock is the only way.
You'll still get the full summary for however far you got — pace gap, lengths completed, average heart rate — and the swim is saved to Health. The only time you go straight back to Setup is if you stop during the Get Ready countdown, before the set has begun.
No — the display doesn't rotate. LapPacer is meant to be worn on the wrist, where the display is already correctly oriented, so there's no rotation control to set.
No. LapPacer works entirely offline, has no servers of its own, and never transmits any data over the network.
Lengths must always divide evenly by the number of segments, so each segment covers a whole number of lengths. Setup automatically snaps both values to the nearest valid combination as you adjust them.
Setup has several rows of +/− buttons packed into a small screen, and a swipe that starts anywhere near one can register as a tap on it instead of a scroll. Turn the Digital Crown to scroll through the list instead — it doesn't have this problem, since it isn't a touch gesture at all.
LapPacer is free on the App Store. It's built and maintained by one person; if you find it useful, consider a small tip to help support development, hosting, and the annual Apple Developer Program fee.
LapPacer is provided “as is”, without warranty of any kind, express or implied, including but not limited to the implied warranties of merchantability, fitness for a particular purpose, and non-infringement. In no event shall the author be liable for any claim, damages, or other liability arising from or in connection with the app or its use.
LapPacer is a training aid, not a safety device. It does not monitor your wellbeing and cannot summon help. Never swim alone, and never rely on it in place of your own judgement or a lifeguard.
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