My new favorite app tracks the amount of exercise I get with remarkable accuracy, and I don’t have to do anything but turn it on. It’s called Moves, and it logs time spent walking, cycling, and running—as long as I’ve got my smartphone with me, which I always do. It’s dead simple, requiring no manual data entry or extra strap-on gadgets to take in my movement data and display it for me in a way that’s easy to understand and analyze.

Created by a startup called ProtoGeo, Moves is free and currently available only for the iPhone (the company plans to release an Android version but hasn’t said when). The app’s precision and power consumption need work, but I’m convinced its simplicity represents the future of self-tracking.

Even if, like me, you get plenty of exercise, having an accurate record of that activity can be compelling. Moves helps me better regulate my levels of activity and keeps track of all the “lost” miles riding and walking around town apart from my daily commute. And, to be honest, it makes it easier to decide whether to indulge in another cheeseburger at the end of the week.

ProtoGeo is among a growing number of companies working to make self-tracking on smartphones easier by taking advantage of the devices’ built-in sensors and GPS technology. The results can reveal insights about your habits and help provide motivation to improve them.

Google Now, for example, already tracks your walking and cycling, which are summarized in a monthly notification (see “Google Now Becomes a Fitbit Competitor by Tracking Exercise”). Placeme, an app from Alohar Mobile, automatically records your destinations (see “New App Watches Your Every Move”)—helpful for remembering that great new sushi place you visited on a trip out of town—and Alohar’s technology is being used in other apps as well. As these apps get better at pinpointing locations and differentiating between types of activities, and less apt to shorten your smartphone’s battery life, I expect we’ll see many more of them. They offer a much simpler, and therefore more powerful, way to track your own behavior.

Moves shows the potential of this trend: it’s nicely designed, it’s easy to use, and it does what it promises without expecting much (or anything, really) from the user. For iPhone owners interested in keeping an eye on their daily activity but not motivated enough to invest in a Fitbit or FuelBand, it’s an awesome solution, especially since you probably have your phone on you most of the time anyway.

The app is simply laid out, with bubbles at the top offering daily activity summaries (tapping them lets you switch between seeing, for example, how far you walked, how much time you spent walking, and how many steps you took). Lower down, a time line neatly illustrates those activities, noting where you started, when you began each activity, how long it lasted, and where you ended up.

Tapping on any activity yields a map showing your routes in colors that correspond to the mode of transportation you used. If you want, you can teach Moves where your home and office are and tell it which specific places you visited; it will then accurately note those destinations on your time line.

Moves nearly always distinguished correctly between walking, biking, and running. In a few cases it wasn’t sure how I was getting around, so it just tagged that time with the generic label “transport.” Usually this happened when I was driving, but if I was walking, biking, or running, I could just say so.

The biggest drawback of Moves is that its location sensing isn’t marksman-accurate. Though the color-coded map routes tended to show the right path across town, Moves also seemed to believe I have a penchant for cutting across railroad tracks on foot and riding through grassy fields on my bike, and occasionally for turning in drunken circles.

More seriously, I noticed that it sometimes recorded my biking distances inaccurately. For example, over two weeks, it logged my daily commute to the office as between 3.9 and 4.4 miles—never the 4.7 miles I’ve measured on MapMyRide. A longer road ride that measures 42.4 miles on MapMyRide was recorded by Moves as 40.5 miles one weekend and 34.5 miles the next, though I took the same route each time. These discrepancies matter if you spend a lot of time in the saddle. For lengthy rides, my Garmin Edge 500 GPS biking computer is far more accurate—but unlike an iPhone, it’s only going to track my rides.

As I’ve suggested, I also noticed that my iPhone’s battery drained faster than usual when I used the app. While Moves smartly does most of its data processing remotely on ProtoGeo’s servers, it would be better if it were more power efficient.

Still, Moves usually knew where I was going and generally did a good job of determining how far it was, how I got there, and how long it took. And while my phone required recharging earlier in the evening than usual, it wasn’t bad enough to cause me to turn off the app.

Despite some drawbacks (which I hope are solvable), Moves should win users and inspire other app makers to develop less cumbersome self-tracking apps. After all, why use another gadget to track this stuff if you’ve already got a powerful, sensor-filled smartphone in your pocket?