Shift - Jet Lag Sleep

Land aligned. Shift uses your Apple Watch wrist temperature to estimate your body clock and adapts your light, sleep, and caffeine cues as your body responds.

Most jet lag apps prescribe a plan on day zero and then forget about you. Shift is different. It uses your Apple Watch wrist temperature — the data your watch already collects every night — to estimate where your body clock actually is, and adapts the protocol every morning as your body responds.

A sleep copilot for people who fly often • Plan a trip, get a day-by-day light, sleep, caffeine, and meal protocol before, during, and after the flight. • Each morning, Shift re-fits its model against last night's wrist temperature, heart rate, HRV, and sleep midpoint, and rewrites the next three days of cues. • See your current body time alongside local time, with an honest confidence interval — "estimated ± 42 min" beats a fake-precise readout. • A predicted alignment timeline shows when your body is expected to catch up. • Between trips, Everyday mode keeps your rhythm steady and shrinks the social jet lag that builds up at home.

The science • Wrist temperature is a clinically supported proxy for core body temperature minimum (CBTmin) — a gold-standard circadian phase marker. • Light cues follow the published Phase Response Curve: morning bright light to advance eastward, evening light to delay westward. • Adaptation rate is learned per user with a Bayesian update after every trip. Eastward and westward speeds are tracked separately — most people adapt 30–50% slower eastward, and the protocol reflects that.

For frequent flyers • Designed for people crossing 4+ time zones at least 6 times a year — international consultants, investment bankers, salespeople, expat executives, crew, touring musicians. • Works best with Apple Watch Series 8 or newer (the first model that records wrist temperature). Without one, Shift uses population estimates and wider confidence intervals. • iPhone 12 or newer for the on-device model.

Privacy • Everything runs on your phone. No accounts. No servers. No analytics SDKs. • HealthKit data stays local. Shift only reads — never writes back to Health. • Trip data is yours to export as PDF for medical records, expense reimbursement, or your own files.

Access • Starter access includes a single-trip protocol preview. • Trip Pass unlocks a 14-day full protocol, reminders, and cue logging for a single trip. • Shift+ adds unlimited trips, real-time phase tracking, Everyday mode between trips, your weekly report and adaptation profile, PDF export, the Watch app, and Family Sharing where available. • Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ • Privacy Policy: https://w3h9uf.github.io/shift/privacy.html

Wellness, not medical. Shift does not diagnose or treat any condition and is not a substitute for medical advice.