Pillow can record sleep sessions both manually and automatically (automatic mode requires an Apple Watch).
To start a sleep session manually:
Using the Apple Watch and the iPhone
Open Pillow on the iPhone.
Open Pillow on the Apple Watch.
Swipe horizontally to access your alarm presets.
Tap on "Start" on the alarm preset you prefer.
Place your iPhone on the nightstand and keep your Apple Watch on your wrist.
When the alarm goes off, please press "Stop" on your Apple Watch.
Using the iPhone or iPad only
Open Pillow on your iPhone or iPad.
Tap on the alarm icon in the bottom left corner.
Tap on "Start" on the alarm preset you prefer.
Place your device on the mattress near your pillow.
Using the Apple Watch only
Open Pillow on your Apple Watch.
Swipe horizontally to access your alarm presets.
Create a new alarm preset or edit an existing one by tapping on the three dots "..." in the top right corner.
Turn OFF all features that require the iPhone:
iPhone Speaker,
iPhone Vibration,
Sound recordings,
Sleep aid.
Tap on Done.
Tap on "Start" to start an Apple Watch-only manual sleep session.