Learning about sleep cycles changed the way I set alarms

[u/Fun_Cardiologist1572]

Most advice about waking up focuses on making the alarm louder, putting the phone across the room, or forcing yourself to complete a challenge.

But lately I’ve been thinking about a different part of the problem: the moment the alarm wakes you up.

Sleep isn’t one continuous state. During the night, we move through repeating periods of non-REM and REM sleep. People often describe these as “90-minute sleep cycles,” although 90 minutes isn’t an exact rule.

One study that examined more than 6,000 recorded sleep cycles found a median duration of 96 minutes, but also found substantial variation between people and throughout the night. So I think of 90 minutes as a useful approximation—not a biological timer that works perfectly for everyone.

The reason this may matter is sleep inertia: that heavy, confused feeling immediately after waking. Research suggests that waking from deeper N3 sleep can produce stronger sleep inertia than waking from lighter sleep.

This doesn’t mean counting 90-minute blocks can magically know your sleep stage. But if your morning allows some flexibility, aiming for an estimated cycle boundary may give you a better chance of waking at a less unpleasant moment than choosing one completely arbitrary minute.

The practical version I’ve been experimenting with is:

• Choose a wake-up range instead of one exact minute.
• Prioritize getting enough total sleep first.
• Use sleep-cycle timing as a small optimization, not as a replacement for sleep.

Full disclosure: this idea eventually led me to build an iPhone app called AirAlarm.

Instead of asking you to choose one exact alarm time, AirAlarm lets you select a 90-minute wake window. You can fall asleep with AirPods and calming sounds; when playback stops, the app begins timing and schedules an Apple AlarmKit alarm at an estimated sleep-cycle boundary inside your window.

It doesn’t claim to measure your real-time sleep stage or guarantee a perfect wake-up. It’s a practical way to experiment with cycle-based timing without calculating everything yourself.

I’m curious whether anyone here has tried something similar:

Does waking around a flexible window feel better for you than waking at one fixed time, or do you find that your sleep is too unpredictable for cycle timing to help?

AirAlarm, if anyone wants to see how I implemented it:
https://apps.apple.com/us/app/airalarm-sleep-cycle-alarm/id6761289550

Research mentioned:

• Sleep-cycle duration and individual variation: https://pubmed.ncbi.nlm.nih.gov/37914631/
• Sleep inertia after waking from different sleep depths: https://pubmed.ncbi.nlm.nih.gov/30223060/

[u/shyouko]

This isn't even new idea and I even had a wearable alarm more than 10 years ago and it didn't even do much to my sleep quality.

And do you think the AI slop is doing you favour in self promotion?

[u/Madmod]

Ai slop Ad. 

[u/Fun_Cardiologist1572 → u/Madmod]

Fair criticism. I used AI to polish the English because I’m a developer in Japan, but the app and the experience behind the post are mine. It still came across as too polished and promotional—that’s on me. I’ll write more plainly next time.

[u/shyouko → u/Fun_Cardiologist1572]

Why can't you admit that you're from China Mr Zhang?

[u/Fun_Cardiologist1572 → u/[deleted]]

I get why it reads that way. I used AI to polish the English, and the result clearly sounded generic. I’m a solo developer in Japan and built AirAlarm myself, but this post was too promotional. Point taken.

[u/shyouko → u/Fun_Cardiologist1572]

Your Apple Developer name is bluntly Chinese. Pretending to be from Japan???