Fitness tracking is one of the Apple Watch’s most popular features, and this fall it is introducing sleep tracking for the Watch. When it launches, it will roll out to tens of millions of users. (Apple will likely soon pass 100 million cumulative Watch sales, if it hasn’t already.) Oura, meanwhile, is approaching 200,000 rings sold.

In the last 10 years there have been mobile apps and smartwatches and bed straps that promise to capture how well we are (or aren’t) sleeping.