Circada

Shift work apps hand you general sleep advice. Circada works with your actual rota. You enter your shifts — early, late, night, off — and it predicts how alert you will be, hour by hour, including the dip that arrives at 4 am.

The engine is the two-process model: a sleep pressure that builds while you are awake and drains while you sleep, plus a body clock that does not simply follow your rota. A phase response curve decides how far your clock shifts each day from light or darkness, and caffeine runs through the model as first-order pharmacokinetics with a half life. Out of that comes a concrete plan: when to sleep, how long to nap, when to seek light, when to wear shades on the way home, and how late your last cup can be.

WHAT IT DOES

• Alertness now and per hour, with the low points named
• A forecast for 4 am and for every hour of your shift
• A sleep and nap plan per day, fitted to the next shift
• Light and darkness advice to shift your clock or hold it
• Caffeine window: how many mg on board and when the last cup is
• A week view with your rota and the alertness you can expect
• Five languages and a glance with the next action

WHAT IT NEEDS

• Nothing. Everything is worked out on the watch: no phone, no account, no internet
• Circada is a planning aid, not medical advice for a sleep disorder