Whether you're curious about a device you purchased or want to see how well a phone runs before you sell it, here are the best diagnostic tools for iOS and Android.

Wondering if your smartphone is in good health? Whether it's a used phone you just bought or an old device you're looking to sell, you can put it through a series of diagnostic tests. Some Android devices have built-in diagnostic tools, but the App Store and Google Play Store offer third-party diagnostic tools, too.

Apps like Phone Doctor Plus, Phone Diagnostics, Phone Check and Test, and TextX can run a battery of tests to check the touch screen, audio, video, camera, microphone, sensors, and other components of your phone. Here's how they work.

Samsung’s line of Galaxy smartphones has a built-in diagnostics tool that's accessible from the keypad. Open the Phone app and tap Keypad, then type *#0*#. A diagnostic screen pops up with buttons for a variety of tests.

Tap Red, Green, or Blue to test those pixel colors. Tap Receiver to check the audio, Vibration to try the vibrating feature, or Sensor to test the accelerometer and other sensors. You can also tap Touch and then move your finger around the screen to test the touch screen, or tap Low Frequency to test low-frequency sounds.

After your test is done, touch the screen or tap the back button to return to the main screen. If you tap the back button from the main menu, you will be returned to the Phone app.

Samsung offers its own free app known as Samsung Members(Opens in a new window) , which can be downloaded from Google Play. It provides sales and technical support, and a built-in diagnostics tool as well. Open the app and tap the Diagnostic button on the home screen.

Tap the individual icons to run diagnostic tests on the battery, SIM card, sensors, touch screen, flashlight, camera, microphone, speaker, Bluetooth, Wi-Fi, and more. Alternatively, tap the Test all button to perform all the tests one after the other. If the test is successful, a checkmark appears on its icon. 

Motorola phones can use the Device Help(Opens in a new window) app, which comes preinstalled on some devices. Open the app and tap Device diagnosis. Choose Troubleshoot to test the touch-screen display, battery, audio, camera, connectivity, and more.

Select Hardware test to run diagnostics on the display, backlight, touch screen, multi-touch capability, flash, front and rear camera, and the proximity sensor. Run a test by tapping the icon for the feature you want to run. You can tap Full Test at the Hardware screen to perform all available diagnostics.

Geared for iOS(Opens in a new window) and Android(Opens in a new window) , Phone Doctor Plus starts by showing you a list of different tests to run, including those for memory, CPU, speaker, microphone, Wi-Fi, Bluetooth, GPS, touch screen, camera, charging, and many more. Tap the Play button to run all the tests or swipe to the left to view a list of all available tests you can run individually. The app then displays the results of any tests.

The app also provides a Status screen that displays your battery charge, available storage, free memory, and network bandwidth. It also researches and displays the trade-in value of your phone. The Android app also kicks in an inventory report that makes sure all the phone’s components are original and a battery health test to check the status of your battery.

Available for iPhone(Opens in a new window) and Android(Opens in a new window) , Phone Diagnostics offers a range of tests to check your touch screen, camera, speaker, microphone, Wi-Fi, cellular access, and many other components. Just tap the button for the test you wish to run or tap Start to run all the tests one after the other.

The multi-touch test asks you to place three fingers on the screen. The camera test snaps photos using the front and rear cameras, while the video record test shoots a quick video using the rear camera. The motion test asks you to move your phone around, and the GPS test verifies your location on a map.

The app doesn't generate any reports or results, but each successful test turns its button green, while a failed or interrupted test appears in red. The app can also attempt to steer you to a repair shop should your phone need to be fixed. The basic version is free with ads, but you can pay $1.99 to go ad-free.

Designed for Android, Phone Check and Test(Opens in a new window) lets you trigger a comprehensive series of diagnostics on your device. The app starts with an overview to explain how it works, how to run its various tests, and what each test encompasses. A monitor screen shows you the current usage for memory, storage, battery, Wi-Fi, and cellular.

To run the guided tests, select the features you want to include. The app can check your battery, network connectivity, audio, display, touch screen, GPS, camera, and sensors, among other features. Some of the tests run automatically, while others require your input.

After each test, you can tap OK if your phone passes or Not OK if something raises a red flag. You can also skip any test and move to the next one. A summary screen then displays the results of each test.

Designed for the iPhone (and iPad), the free TestX(Opens in a new window) app can run diagnostics on your phone's touch screen, earphones, speaker, microphone, accelerometer, compass, Wi-Fi, Bluetooth, battery, sensors, camera, and flash.

The app offers a lot of flexibility to run the various tests. You can choose Quick Scan to check key features or tap Full Scan to check everything. Alternatively, you can perform all the tests within a certain category or just run a specific test.

A green circle shows a test that has been completed successfully. After you’ve run the necessary tests, you can generate a full report to see the results. As a bonus feature, the app provides password-protected access to notes, files, photo albums, and other content that you may want to create and secure.

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I've been working for PCMag since early 2016 writing tutorials, how-to pieces, and other articles on consumer technology. Beyond PCMag, I've written news stories and tutorials for a variety of other websites and publications, including CNET, ZDNet, TechRepublic, Macworld, Popular Science, Time, Fortune, US News & World Report, and AARP Magazine. I spent seven years writing breaking news for CNET as one of the site’s East Coast reporters. I've also written two books for Wiley & Sons—Windows 8: Five Minutes at a Time and Teach Yourself Visually LinkedIn.

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