Some of the things smartwatches and activity trackers can measure are pretty unusual—such as fertility and sun exposure—while others are endlessly useful.

Fitness Trackers

When it comes to the vast majority of wearable tech, there are two basic categories: fitness trackers (also known as activity trackers, and most commonly identified with the brand Fitbit) and smartwatches. Not all wearables fall under one of these two boxes, but here we’ll focus on these two categories.  Let’s start by taking a look at all the things you can track with a wrist-worn or clip-on fitness tracker. Note that this list doesn’t necessarily include all the granular stats you’ll find on more specialized sports wearables, such as swimming-specific wearables or those used by serious athletes.

Steps

This one’s probably familiar to you, as pretty much any activity-tracking device includes step tracking. Activity trackers, smartwatches, and many smartphones include accelerometers that can measure your movement and, in turn, deliver you stats like steps-per-day. You’re probably familiar with the benchmark of 10,000 steps per day (equal to a bit less than 5 miles). Pretty much any tracking device, even the clip-on Fitbit Zip, can help you monitor your progress to this goal or any other personal goals you’ve set for yourself. 

Distance Traveled

It only makes sense that if a wearable device tracks steps taken, then it can show your total distance traveled, as well. This metric is also available courtesy of a gadget’s accelerometer, and you can find it on pretty much any activity tracker, from a sub-$50 option such as the Xiaomi Mi Band to specialized sports watches from brands like Garmin.

Floors Climbed

Activity-tracking wearables that include an altimeter can measure how many flights of stairs you climb and other elevation-related data. And if you live in a hilly city, you might be surprised to see how quickly those flights add up over the course of a day!

Calories Burned

Keeping tabs on the number of calories burned during a workout can be quite useful, especially if you’re looking to lose weight. Luckily, this metric is yet another “entry-level” fitness stat for fitness trackers, so you should find it on virtually every option that makes its way onto your comparison-shopping list.

Active Minutes

Most activity-tracking bands or clip-ons also gather data on your total active minutes in a day, and you’ll be able to view this stat on the device’s companion app. For instance, with Fitbit trackers, you can view your total minutes for specific workouts (with dates listed for each). This brand of devices also monitors your hourly activity stats and stationary time, and they include reminders to get up and move when you’ve been sedentary for an extended period of time.

Specific Exercises or Activities

By monitoring patterns across the three axes measured by their accelerometers, fitness trackers can identify the type of activity you’re engaged in. For example, with Fitbit devices that support the company’s SmartTrack feature, your workout will be automatically identified as one of the following (if applicable): walking, running, outdoor biking, elliptical and swimming (though only specific devices are water-proof). Plus, devices like the Garmin vivoactive can even identify less mainstream activities like golf.

Sleep Time and Sleep Quality

Not everyone wants to wear an activity tracker to bed, but plenty of these wearables do have sleep-tracking technology built-in. Devices such as the Jawbone UP3, Basis Peak and Withings Activité monitor your movements using sensors, and this data is translated into information about your sleep behavior during a specific period. For example, if you were to wake up frequently in the middle of the night, a wearable device would track the periods when you sit up or stir and track those time frames as awake periods that don’t count toward your total sleep time. This way of tracking sleep is called actigraphy, and while it’s not the most accurate way to measure your Zs (measuring brain waves is less convenient, but more precise), it can give you some insight into your habits.

Heart Rate

Especially if you’re a runner, you might be interested in keeping tabs on your heart rate—both your resting beats per minute and your rate when you’re mid-workout. Not all activity trackers include this functionality, but several do, from the Samsung Gear Fit to the Garmin vivosmart HR. Note that built-in heart rate trackers on fitness bands aren’t widely believed to be as accurate as chest strap heart rate monitors, so if you need the most precise measurement possible, you might want to consider this latter option instead.

Fitness Score

On its Charge 2 device, Fitbit offers a feature for measuring your fitness levels compared to other people of the same age or gender. This “cardio fitness score” is a measure of your cardiovascular fitness based on your VO2 max (the maximum amount of oxygen your body can use when you’re working out at your highest intensity), and it’s found under the heart rate section of the Fitbit app. You’ll fall into one of several categories, from poor to excellent. 

Workout Routes and Pace

Some wearables—generally the more sophisticated and expensive ones—include built-in GPS for mapping your runs, walks, jogs, and other types of workouts. Built-in GPS also comes in handy for displaying your pace, split times distance in real time, meaning it’s especially useful for athletes training for a race.

Smartwatches

Unlike fitness trackers, smartwatches focus on bringing smartphone-style alerts right to your wrist, so you can view info such as incoming texts, calls, emails, and upcoming calendar events at a glance. That doesn’t mean they can’t track activity metrics as well. Below we’ll detail some of the metrics that are trackable via smartwatch. As you’ll see, if you’re only interested in the more basic activity-tracking metrics, a smartwatch could very well pull double duty and eliminate the need to buy a separate device like a Fitbit.

Steps: Most smartwatches include an accelerometer to track basic activity metrics such as steps taken. Distance Traveled: Ditto with steps taken; most smartwatches will track your distance traveled, as this is a relatively standard activity metric that doesn’t require a more specialized sensor. Calories Burned: All Apple Watch models track calories burned, and users can view this data through the Health app. Most smartwatches should be able to track this stat and display it, provided you have the right app, since tracking calories burned only requires a wearable with an accelerometer. Heart Rate: Available on devices such as the Apple Watch Series 1, the Apple Watch Series 2, the Huawei Watch, the Motorola Moto 360 Sport. GPS Location: Available on gadgets such as the Samsung Gear S3, Apple Watch Series 2, the Motorola Moto 360 Sport and countless running watches from brands like Garmin.

Specialized Wearables

While the two previous sections will be the most interesting if you’re shopping for a multi-purpose wearable, if you have the cash to spare or are simply curious about what else a wearable can track, this section is for you. These weirder, more specialized devices go beyond the standard activity metrics to tackle different aspects of wellness.

Diabetes Risk

Some day in the not too distant future, we could see commercially available wearables that measure a user’s glucose levels. Already, however, you can buy a pair of temperature-monitoring socks from the brand SirenCare. These wearables are meant to prevent diabetic foot ulcers by tracking foot temperature.

Fertility

Those looking to conceive will find specialized wearables marketed toward them. One example is Ava, a bracelet that monitors fertility by measuring things such as skin temperature, breathing rate, and heat loss. 

Sun Exposure

For those of us who are perpetually terrible at remembering to apply or reapply sunblock, there are quite a few UV-sensing wearables that can help keep you protected. For instance, the June bracelet aims to prevent premature aging by measuring your exposure to harmful rays, in addition to displaying the current UV index in real time.

Bottom Line

While most of us think of step- and calorie-tracking Fitbits and Jawbone devices when we think of wearables, the fact is that activity trackers and smartwatches go far beyond these basic stats. Whether you want to get in shape or monitor a specific wellness-related issue, chances are there’s a gadget for you.