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The interval from the instant the start tone sounds to the instant you react — either your tap on the screen or the moment motion detection picks up your movement. Because the timing uses a monotonic clock, numbers recorded on different days are directly comparable.

No. The gap between the "Take your marks" command and the start tone is randomized on every rep. If you could memorize the timing and anticipate it, the drill would stop being a drill. You can change the range of that delay in Settings.

Any rep where you react before the start tone is recorded as a false start, the same way it would be treated in a meet. In your history it's marked separately from a clean rep, and false starts are tallied for you.

Touch suits quick, repeated reps you run by hand. Motion suits practice that mirrors your actual takeoff — you set the device on a starting block or similar surface and it detects your reaction from the movement. Pick whichever fits your training setup.

Yes. It's a standalone Apple Watch app, so you can leave your iPhone in a bag or locker and still practice, review records, and change settings entirely from your wrist. The signal comes through as both sound and haptics.

No. Records are stored only on the device you're using and are never sent anywhere. Please note that deleting the app also deletes those records.

No. SwimStart is a training tool. It measures your reaction to a signal produced by your iPhone or Apple Watch, and it is not a substitute for official starting equipment or competition timing systems.