Circadian rhythm alarm for Android: an alarm anchored to sunrise

What a circadian rhythm alarm is

"Circadian rhythm alarm" is what people call an alarm tied to the sun rather than to the clock. The word comes from the body's roughly 24-hour cycle; in an app store it simply means the alarm follows sunrise instead of staying at a fixed time.

In Risetime, the moment of the sun you choose is called an anchor — sunrise, solar noon, sunset — and the distance you keep from it is the offset.

How much sunrise moves through the year

Local time, 2027, computed with the same astronomical library the app uses.

A fixed alarm at 06:30 in London therefore rings 1 h 47 after sunrise in June, and 1 h 33 before it in December. Same alarm, two different mornings.

How to set a circadian rhythm alarm

1. On the Alarms tab, press +.
2. In the menu at the top, pick Sunrise.
3. Leave the dial where it is to wake at sunrise, or turn it to the distance you want — 30 minutes before, an hour before.
4. Press OK. Then open the alarm in the list and tick Repeat to choose your days.

The distance you set never changes. Sunrise does, and the alarm goes with it — through the equinoxes, the solstices and the daylight-saving switch. How to set a sunrise or sunset alarm on Android

A day that follows the sun — and a clock

Here is the day I actually run, on my own phone:

There is a sixth, eight hours before sunrise, to start winding down. It is switched off at the moment — the middle position of the switch keeps an alarm without letting it ring.

That's six alarms, one of them off — more than the free three.

The sun-anchored ones follow the light; the clock ones hold the things other people expect of you. Both live in the same list, and each card says which is which.

How far this goes depends on where you live. In Sydney, sunrise moves by about an hour across the year and a sun-anchored day barely drifts. In London it moves by more than three, so the morning follows the sun while the working hours stay on the clock.

When sunrise comes too late

In midwinter, sunrise arrives after the working day has begun — 08:03 in London on 21 December. Two ways round it:

• Wake at first light instead. Light comes well before the sun does. In Settings → Anchors, make your own anchor at civil dawn — the point where there is enough light to see outdoors without a lamp — and set your alarm on that. Custom sun angles and twilight anchors
• Keep both kinds of alarm, as above: the clock for the days that start at a fixed hour, the sun for the rest.

An alarm, not a sleep tracker

Risetime does not track your sleep. It does not record when you dismiss an alarm, it has no account, no cloud and no analytics. It has no internet permission at all, so the operating system itself stops it from connecting: sunrise times are computed on your phone, and your location never leaves it. That is also why it works in airplane mode, in a valley, on a boat. Privacy policy

Risetime is free for up to three alarms and three timers — for good. Need more? Use those three first, and see if it's worth your support: supporters get unlimited alarms and timers, yearly or once. If not, I'll be happy to hear you out.