How would you determine sleep from cellphone data?

Clarifying questions:

For whom, we are determining sleep? Child, adult or old age person? Up to you

Sleep means deep sleep or light sleep? Both

We are using cell phone or cell phone with wearable also?  Only cell phone

Description of cell phone data:

 Sleep tracker in Cell phone generates data from three sensors:

1.       Accelerometer: it detects movement. It knows when you pick up your phone. If it detects long stretches of time, it infers that you might be asleep when combined with input from other sensors.

2.       Light sensor: the cell phone detects ambient light and use it to adjust screen brightness. It is used to detect when you are in dark room, presumably asleep. Combined with accelerometer.

3.       Microphone: detect ambient sound. This sound is different than commands or requests, that send data to voice recognition server to be analysed. The ambient noise is processed locally to detect dB levels.it is used to indicate if there is activity in the room.   

Wearable measures heart rate also to assess whether you are sleep or awake.

So, we can determine sleep from cell phone data on the basis of data generated from three sensors: Accelerometer, Light sensor and Microphone.