The Best Heart Rate Monitor Apps
Credit: NicoElNino/Shutterstock.com

Your smartphone has a secret superpower: With its camera and flash alone, it can measure your heart rate. That means that apps are available to track your heart rate, with the aim of helping you improve your health.

This simple process has a complicated name: photoplethysmography. Every time the heart sends a pulse of blood through the body, the tiny capillary vessels in the skin expand. When a smartphone's flash illuminates the skin, its camera can capture the miniscule color changes that happen each time the heart beats. (Because you have to hold fairly still for this process, these apps don't provide the sort of continuous monitoring that external heart rate monitors can provide; with these apps, you'll have to stop what you're doing for about 10 seconds to take your pulse.)

Dozens of heart rate monitoring apps take advantage of smartphones' built-in ability to provide a quick and easy way for users to take their own pulse — no math required. We recommend looking for one of these apps. Some heart rate monitor apps on the market require users to take their own pulse, tapping their fingers on the screen with each heartbeat. A few are simply timers that do little more than tell you how long to count your own heartbeats. There is little point to downloading these apps, as they don't save much trouble over simply taking your own pulse.

Why measure your heart rate? Knowing your heart rate can provide you with helpful information about your health, according to the American Heart Association (AHA). Changes in your resting heart rate can signal a medical problem, according to the organization, and the number of times your heart beats per minute can hint at your fitness level. For most people, the number lands between 60 and 100 beats per minute.

Likewise, exercisers may want to measure their heart rate to see if they're working hard enough. A good target is 50 to 85 percent of your maximum heart rate, according to the AHA. Your maximum heart rate is approximately 220 minus your age.

Instructions in the Instant Heart Rate app tell you how to measure your heart rate with your phone.
Instructions in the Instant Heart Rate app tell you how to measure your heart rate with your phone.
Credit: Stephanie Pappas for Live Science

Of the apps that measure your heart rate for you, our favorite is the popular Instant Heart Rate app, developed by Azumio (iOS and Android, free).

The Instant Heart Rate app tells you when it's detecting your heart rate.
The Instant Heart Rate app tells you when it's detecting your heart rate.
Credit: Stephanie Pappas for Live Science

We tested the app by comparing its results with manual pulse-taking, and found that it was quite accurate — within a beat or two per minute. The app also lets you record your heart rate and tag each measurement with details about what you were doing at the time, ranging from "just woke up" to "exercising" to "resting." An additional "notes" section allows for even more customizability. The app is very easy to use, with clear instructions and a simple interface, and it can be set to remind you to measure your pulse with push notifications. A heart rate target zone calculator is included. The ads in the free version are unobtrusive.

The downside to the free version of Instant Heart Rate is that you can save only your five most recent measurements. However, you can save older records by downloading and syncing your data with Azumio's free fitness app, Argus, or by manually exporting the data in a .CSV file. Or, to save more than five measurements, you can get the paid version of the app, Instant Heart Rate Pro ($1.99). A pro upgrade also gets you graphs of heart rate trends over time, and nixes the ads.

Runner-up

A close competitor for our pick for the best heart rate monitor is Runtastic Heart Rate Pro ($1.99 iOS, Android). The app works the same way as Azumio's version and appears equally accurate. Runtastic stores your last 10 measurements in handy graph and list format. It provides less detail for tagging measurements, but you can enter whether you measured your heart rate while resting, before or after exercise, or at your max heart rate. You can then filter the data using these tags. (There is also a free version of this app, for those who would like to try before they buy.)

The home screen of the Runtastic Heart Rate Pro app
The home screen of the Runtastic Heart Rate Pro app
Credit: Stephanie Pappas for Live Science

The app includes a reminder feature and the ability to share results via Facebook, Twitter or email. If you have a Runtastic account, the app will automatically sync your heart rate data with your online user profile. If you have other Runtastic apps, all of that data ends up in one convenient place.

For some users, these pushes to share your info on social media sites may be more annoying than helpful. And it's irritating that even with a Pro upgrade, Runtastic's app pushes pop-up ads begging for 5-star reviews or asking users to download the company's other apps. These factors, more than the app's actual functionality, pushed Runtastic Heart Rate Pro down to No. 2 on our list.

Other good apps

Because they are fairly simple, heart rate monitors are sometimes integrated into multipurpose apps. These apps — often workout trackers — have their own pros and cons. But one multipurpose option we like is MotionX 24/7 ($0.99 iOS). This app is part pedometer, part sleep tracker and part heart rate monitor.

For a low price tag, MotionX 24/7 offers nice functionality on all three fronts. The heart rate monitor feature is simple to use and offers nice stats, including weekly and monthly averages, lows and highs. The app records the time and date of each measurement, but doesn't offer options for tagging entries with user activities at the time. As a result, this app is probably best for people interested in tracking a specific heart rate measurement, such as their resting heart rate, or heart rate during exercise.

MotionX 24/7 also lets you log exercise and body weight, keeping your health data organized in one place. Its sleep tracker includes a motion sensor and a microphone to detect snoring or sleep talking, and the app includes a smart alarm intended to wake you gently.

Heart Rate ($0.99, iOS),from Sport.com, is another fine app — and this one has a twist. As well as measuring your heart rate with a finger over the camera, this app lets you use your smartphone's front camera to measure your heart rate in your face. Simply hold the phone in front of your face, centered over the app's face icon. The icon will turn green when your face is properly centered.

Our tests of the front camera function showed that this heart rate measurement was accurate, albeit tougher to get than if you were using the back camera and a finger. You'll need to be in bright light and hold very still, without talking. Still, this is a nice feature to have in case you don't want to smear a sweaty finger all over your camera lens while working out.

The Heart Rate app also offers a history log and nice graphs for tracking heart rate over time. Occasional pop-up ads with an elusive "X" button are a downside.

A screen from the Cardiio app
A screen from the Cardiio app
Credit: Stephanie Pappas for Live Science

Like Heart Rate, Cardiio ($0.99 iOS) has options to measure your heart rate from your finger, via the back camera, or from your face, via the front camera. This app keeps 30 days of records, exportable in a CSV file. It also includes a cute cartoon cardio workout, consisting of seven minutes of exercises meant to get your heart pumping. The exercises aren't complicated (they include jumping jacks, wall sits and lunges), but they're a nice little bonus on an otherwise simple app. One fun aspect of Cardiio is that it offers you comparisons for where your heart rate falls compared to, say, Olympic swimmer Michael Phelps' resting heart rate, or the average resting heart rate of people living on the island nation Mauritius. In-app purchases will get you age/gender comparisons, a target heart rate zone calculator and other add-ons.

Another option for those who'd like to measure heart rate from the face is Azumio's Cardio Buddy (Free, iOS). This app is not designed to measure heart rate from the finger, though a pro upgrade ($1.99) enables users to use the back camera to check other people's heart rates as well as their own. Overall, Cardio Buddy has a nice display and a fun graph feature that compares your heart rate to both the average heart rate in various nations and to those of random animals. (Did you know a goat's resting heart rate averages 75 beats per minute?)

Without the pro upgrade, this app doesn't have too many perks — you can't even export data. But Cardio Buddy's graphing feature, which shows weekly and monthly averages, lows and highs, is one of the easiest to navigate of all the apps we tested.

Offbeat apps

The pplkpr app aims to tell you how you really feel about your friends.
The pplkpr app aims to tell you how you really feel about your friends.
Credit: Stephanie Pappas for Live Science

If you're less interested in fitness and health and more interested in what your heart has to say about your friends, you might want to ditch all of the above and head right for pplkpr (Free, iOS).

This app requires a smartwatch, so it's a bit different from the other apps in this article — but then, that's true on multiple levels. The idea behind pplkpr (which is inscrutable code for "people keeper") is that variability in your heart rate offers a unique glimpse into your emotions. Designed to work with a Mio Alpha or Mio Link wristband, the app purports to determine whether interactions with various friends leave you bored, excited, anxious and even aroused (um, awkward…). If you're the sort of person who conducts your social life based on an iPhone app, you can then curate your friends accordingly. Yay?  

Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.