Soln

Soln is a sleep engine built on cognitive load theory.

Different from other sleep apps

Most sleep apps are just players — they start audio and leave you to it. Soln calculates how hard it will be to fall asleep tonight, decides which layer to start at and how long to stay there, then stops when you're out. You don't have to manage anything.

Five audio layers

· Silent preparation — nothing playing, just space for your mind to settle · Minimal white noise — a steady background to mask outside noise · Heart rate-synced white noise — audio tempo follows your heart rate; as it slows, so does the sound · Tonal fade — frequency gradually drops, sliding your brain from alert to relaxed · Semantic drift — soft, loosely connected speech that gives your mind something to dissolve into instead of looping the same thought (paid)

How long you spend on each layer isn't fixed — it depends on how you're doing tonight.

Apple Watch auto-stop

When you fall asleep, Apple Watch detects it. Soln fades the audio out over two seconds, then stops. No timer to set. No sudden silence to wake you (paid).

Nightly assessment

Before bed, based on today's mood and last night's sleep, Soln estimates how hard it'll be to fall asleep and gives you an optimal bedtime window and expected sleep onset time.

In the morning, three scores: reaction, memory, and mood. Sleep well, score well. Sleep poorly, score reflects that. Straightforward.

Full sleep history

A three-color ring for each night. Long-press any day for that night's detail and sleep-onset timeline.

One-time purchase

Free for 7 days, full features included. After that, a one-time purchase permanently unlocks everything. Tied to your Apple ID — restore on any new device. No ongoing charges.