But the reality of these devices comes nowhere close to the promise. After using yet another unspectacular sleep tracker — this time the much-anticipated Sense, which raised $2.4 million on Kickstarter last year — I was reminded, again, of how fundamentally useless these devices can be.

The Sense works well enough, for what it is. It offers one primary advantage over most other sleep trackers. You don’t have to wear it or remember to keep it charged. Instead, it sits on your bedside table, watching what’s going on in your room. In my week using it, I found a few flaws in the system, though several were prerelease bugs that should be ironed out soon. If you’re in the market for a sleep tracker, the Sense should be on your list.

But why are you in the market for a sleep tracker? Sleep tracking is a little bit bogus. I’m a terrible sleeper, but neither the Sense nor any other sleep tracker has revealed anything particularly helpful about what was happening to me between the sheets. If you’re not sleeping well, you almost certainly know it already, and there’s a good chance you know why. At best, the tracker adds a layer of empirical precision to a situation already evident in your midafternoon yawns.

What do you do with its data? There are many potential reasons for your poor sleep — you’re working too hard, you’re partying too hard, you’re too stressed, you have insomnia, you have a baby, your neighbors are noisy, you suffer some physiological problem — but the sleep tracker isn’t going to be able to fix any of those. As I studied the Sense’s readings every morning over the past week, I was puzzled about what to do next. I knew I had slept poorly; I had gone to bed too late, woken up too early, and I felt terrible. Why did I need a device to prove that? And unless the sleep tracker was offering to take care of my children for me, why should I bother with its data? The Sense comes in two parts that work more or less automatically. There’s a tennis-ball size orb that sits on your bedside table. It remains plugged in to the wall, wirelessly connects to the Internet, and it packs a bevy of sensors. The orb can measure the brightness of the lights in your room, temperature, humidity, the concentration of particulates in the air, and it can also record sound in certain cases, like snoring.

The other part of Sense is the Sleep Pill, a tiny, battery-powered device that attaches to your pillow and detects the movement of your body throughout the night. You can use two Sleep Pills with each Sense orb, letting you track your sleep and your partner’s. The Sleep Pill’s battery lasts about a year, according to James Proud, the founder of Hello, the company that makes Sense. The Pill uses a hearing-aid battery that can be bought at just about any drug store. The Sense, which goes on sale to this week, comes in either a black or white orb, and sells for $129 with one included Sleep Pill. An extra Pill costs $39.

The Sense also has a well-designed app that works on newer iOS or Android devices. The app keeps a diary of your sleep and reports a daily score about how well you slept. The app also lets you set a “smart alarm,” which wakes you up when you’re in the phase of your sleep cycle most conducive to waking up, usually a few minutes before the time you set. This way of waking is supposed to make you feel refreshed, though not by much; if you haven’t slept enough, you’re not going to want to wake up even if the alarm is smart.

The main flaw in the Sense is how it interprets data from two Sleep Pills. I attached a Sleep Pill to my wife’s pillow, and I found that the device often got us confused: When she went to sleep before me, it reported that I had gone to bed at the same time as she did — and it reported that she had woken up when actually I had. Mr. Proud said that this happened because the company hasn’t yet added algorithms to distinguish the movement on each Sleep Pill when two are used. He said an update would be coming soon, but he also said that the Sense’s confusion, in my case, was an aberration — most people will not encounter this problem, he said.

I’m inclined to believe him. But even if the Sense worked perfectly, I’m still not sure that many people need one.