Here is where the AutoSleep app gets credit: It estimates sleep duration and deep sleep using the motion and heart rate sensors, but it does not attempt to guess REM sleep. David Walsh, the computer scientist who developed AutoSleep, said he knew the movement and heart rate sensors would not accurately estimate the REM stage, so he didn’t bother.

Another unknown for sleep trackers are the algorithms that are being used to measure people’s sleep, Dr. Vallat said. In contrast, the algorithms used by university sleep labs have been publicly shared for decades.

Some scientists said consumer-grade sleep trackers should not be dismissed as inaccurate. Michael Grandner, director of the University of Arizona’s sleep research program, who has consulted for Fitbit, said that wrist-worn sleep trackers had a long history of use in scientific research and that some devices could be very accurate at measuring sleep stages. He added that the devices enabled some sleep tracking to be done in the real world, not a lab.

What to do?

O.K., but what happens once you collect your sleep data from a tracker or an app? There is no real answer.

My sleep-tracking statistics said I needed more sleep. (Duh.) Buried deep inside the data was some general information about sleep, but the app stopped short of offering advice on how to solve my personal sleep problems.

Dr. Ethan Weiss, a cardiologist at the University of California, San Francisco, has been wearing a ring on his finger called Oura Ring, which includes a sleep tracker, for nearly a year. The ring measures motion and heart rate to present granular data about the different sleep stages. He said that while the device most likely had a rough sense of when he was sleeping and awake, he didn’t know whether the information about sleep stages was accurate — let alone what to do with it.

“There’s no program — it’s just information,” Dr. Weiss said. “The question is can you do anything on your own to optimize it? Or is the information just worthless or is it making things worse? Sometimes being aware of it just makes you even more anxious.”