What Risetime does — simply and accurately
Risetime does one thing: it calculates the real astronomical sunrise for your location every day and sets a system-level Android alarm to that time. When sunrise drifts with the seasons, your alarm drifts with it — automatically, silently, in the background.
Setting it up takes about two minutes. Here's how.
Step-by-Step Setup
Set your location
Open Risetime and go to Settings. You have two options: grant coarse location permission for automatic detection, or manually enter your city. Either way, Risetime uses your coordinates to calculate sunrise, sunset, and other celestial event times for your exact position on Earth.
Your location never leaves your device. It's stored locally and used only for on-device math. There's no server to send it to — Risetime doesn't have internet permission.
Pick your celestial anchor
Tap the plus button to create a new alarm. You'll see five anchor options:
- Sunrise — the moment the sun's upper edge clears the horizon
- Sunset — the moment the sun's upper edge drops below the horizon
- Noon — solar noon, when the sun reaches its highest point in the sky
- Nadir — solar midnight, the sun's lowest point (not necessarily 00:00)
- Clock — a standard fixed-time alarm, if you need one
Your anchor is the celestial event your alarm tracks. In most latitudes, sunrise drifts by up to two hours across the year — your alarm follows it automatically.
Set your offset
Decide how many minutes before or after your anchor you want to wake up. A few examples:
- Sunrise, no offset — alarm fires exactly at sunrise
- 30 minutes before sunrise — wake up in pre-dawn light, be ready for the sunrise
- 15 minutes after sunset — catch the blue hour
- 1 hour before noon — a mid-morning reminder that tracks the actual middle of the day
The offset stays fixed. The anchor recalculates daily. Your alarm is always exactly where you want it relative to the sun.
Choose which days it repeats
Select which days of the week the alarm should repeat — every day, weekdays only, weekends only, or any combination. You can also set a one-time alarm that fires once and disables itself.
Enable the alarm and you're done. That's it. There is no step five.
What Happens Next
Once your alarm is set, Risetime runs a lightweight background worker every day. This worker recalculates the exact sunrise (or sunset, or noon) time for your location on the upcoming day, applies your offset, and schedules the alarm with Android's system alarm clock API — the same one used by your built-in clock app.
You don't need to open the app. You don't need to be connected to the internet. The recalculation happens automatically, even if you haven't opened Risetime in weeks.
Most days, the best thing you can do with Risetime is forget it exists. It's designed to work without attention.
If you do open the app, you'll see the next alarm time displayed on each alarm card — already adjusted for tomorrow's celestial event. You can verify it's right. But you don't need to.
How Risetime Calculates Sunrise Times
This is where Risetime differs from every sunrise alarm app that looks up times from a web API.
Risetime includes an embedded astronomical calculation engine — a library called commons-suncalc — that computes celestial event times using the same orbital mechanics models used by observatories and maritime navigation. Given your latitude, longitude, and the date, it calculates the sun's position and derives exact event times for sunrise, sunset, noon, and nadir.
All of this math runs on your phone. There's no API call, no server lookup, no internet connection involved. This isn't a fallback or an offline cache — it's the primary and only method. Risetime doesn't have internet permission, so there's no network path even if it wanted one.
This means Risetime works in a cabin in the mountains, on a camping trip with no signal, or in the middle of the Pacific on a cargo boat. Anywhere your phone goes, your sunrise alarm works.
The underlying algorithms — based on Jean Meeus' Astronomical Algorithms — account for standard atmospheric refraction, the bending of light near the horizon that makes the sun appear to rise slightly before it geometrically clears the horizon. The result is accurate to about a minute, which is what you'd see with your eyes.
Because the computation is deterministic — same coordinates, same date, same result — there's no variation between runs and no dependency on an external service staying online. Your alarm is as reliable as the math that predicts where the sun will be tomorrow. And that math has been reliable for a few centuries now.
Tips
- Check your alarm reliability. Open Settings and look at the Alarm Reliability section. Green checkmarks mean Android has all the permissions it needs to fire your alarm reliably. If anything is yellow or red, Risetime tells you exactly what to fix.
- You can mix alarm types. Risetime handles both celestial and standard fixed-time alarms. No need to keep a second clock app for your 9 AM Monday meeting.
- Set multiple celestial alarms. A sunrise alarm to wake up, a sunset alarm to remind you to step outside for golden hour, a noon alarm for a midday break — they all recalculate independently.
- Moving to a new city? Update your location in Settings, or enable automatic location updates. All your celestial alarms recalculate for the new position.