The MySense sleep sensor looks like a black belt with a small box attached.
The sleep sensor is placed on your mattress under your bedsheet and should be laid mid-chest height as you lay down.
The sensor should be kept plugged into the power outlet at all times, even when you're not in bed.
The sensor is triggered by pressure and motion and sends data securely to the MySense home hub to understand sleeping patterns, including movement at night, time to bed, waking time and hours of sleep.
To find out how to install the sleep sensor, read this article.