A threat to your precious data is everywhere, regardless of the platform or device you are using to access it. Smartphones are also the target of hackers, who often release malicious code for different mobile platforms. It's a good strategy to preemptively 
Whenever I purchase a new smartphone, an antivirus app is one of the first and important applications I install on my device. In fact, you should install it before installing any other app.
If you're running a low-end configuration smartphone, pay attention to the lag, an antivirus app may put on the device. In such a case, go for the lightest option built specifically for such devices.
1. ESET Mobile Security for Android
The first one in this list is a solid and reliable antivirus app you can rely on, without giving a second thought. It has a real-time scanning engine that protects your smartphone from the most common infections. The activity log is very handy if you're sharing your smartphone with family members.
The free version includes the remote device lock and remote siren facility, which in itself is quite impressive. It works flawlessly on tablets as well. I loved its reporting feature, which more or less is a kind of health report of your mobile. For the app locking feature, you'll need to upgrade to a paid plan.
Download ESET Mobile Security for Android
2. Avast Mobile Security
Apart from regular virus protection features, this antivirus also protects you from spam and unwanted pesky calls. It also secures apps and photos through different means viz., fingerprint, PIN, and pattern. A VPN makes it a complete security system for your smartphone. I'll happily pay for its premium version.
It's not just malicious websites and apps against which you get protection, but it also verifies if the Wi-Fi network you're trying to connect with is secure or not. Remote data deletion and remote device lock are supported as well. It also provides you with useful app reports to help you keep your phone—healthy.
Avast Mobile Security for Android
3. F‑Secure Mobile Security
Needless to say, it's available both for smartphones and tablet devices. It also protects you from phishing while shopping online. Hazardous or harmful apps are often installed unknowingly by smartphone users. This powerful antivirus has the capability to detect such harmful apps with ease.
Online banking protection is also available through it, giving you peace of mind while doing such types of transactions. It's available in most of the popular languages, giving you a true multilingual antivirus solution. I've used it on my old smartphone with great results. Do once try it and see the difference.
Download F‑Secure Mobile Security
4. Kaspersky Internet Security for Android
An all-in-one security product to give you peace of mind while working and browsing on your Android device. It uses machine learning to better deal with upcoming new threats on the web. Apart from working as a powerful antivirus solution, it's also suitable for keeping your device secure from hackers.
Like other security apps, Kaspersky too offers a powerful anti-theft solution for Android devices. So, if your device is lost, there are very high chances you may get it back through this feature. It can also monitor for spying activities on your device, giving you complete peace of mind from such threats.
Download Kaspersky Mobile Security for Android
5. Norton Mobile Security
It's one of the oldest and trusted brands when it comes to securing your devices connected to the internet. The mobile app offers an array of security features, keeping your Android smartphone completely secure. Its App Advisor feature helps you to prevent the installation of suspicious applications.
It also hardens your Wi-Fi connection to prevent unauthorized connection attempts. It also keeps an eye on app activities and presents the activity log in a presentable way to see what exactly these apps are doing on your smartphone. I'll recommend using this security solution on flagship Android devices.
Download Norton Security for Android
6. BullGuard Mobile Security
It's one of the best free and powerful mobile antivirus and security applications available for Android smartphone users. It has a pretty useful and feature-packed anti-theft module. Optionally, one can also back up the entire phone data on a secure cloud storage account. It has a simple and easy-to-use design.
It also proactively protects the SIM from data wipes or SIM locking. Location and GPS tracking (if required) is also built-in with this app. It also has a security manager enabling you to access your phone from a desktop or from a web browser. It works perfectly with several old versions of Android as well.
Download Free BullGuard Mobile Security
7. Avira Free Antivirus for Android
If you're using Avira antivirus for your Android smartphone, you'll get a free VPN as well. It also includes a space and memory cleaner to keep your phone running in optimal condition. Its identity safeguard alerts you if your email address leaks in a data breach. The app's minimal interface is excellent.
The pro version includes premium features like protection of your smartphone's camera and mic. It enhances your privacy and security by many folds. Remote monitoring of the device helps you recover your lost phone in a quick time. I've used it on my Oppo smartphone for a month with expected results.
Download Avira Antivirus for Android
8. Bitdefender Mobile Security for Android
This one too comes with a free VPN with a generous daily data limit for low to moderate internet users. It's light on battery with a small footprint and works quietly in the background. It works seamlessly on older versions of Android, too. I've tested it (for a week) thoroughly on Android 6 and 7 without any issues.
If you're looking for a premium and affordable antivirus solution for your smartphone, this is one of the cheapest yet fully capable options. You can use it for your Android-powered tablets too. It can also integrate with your smartwatch to give sound alerts either at your will or if you go far from the handset.
Download Bitdefender Mobile Security
9. Google Play Protect
Google's inbuilt Play Protect service is itself the first line of defense against malicious apps and activities. It works quietly in the background, scanning your Android device for vulnerabilities. Its Find My Device service is one of the best in locating your lost phone. You can easily lock and erase the phone, through it.
The best part is that it's free, and you don't need to manually install or activate it. It comes deeply integrated with your Google account on an Android device. You can see it in action while updating the apps, where you can see the apps scanned at so-and-so date. It's Android's inherent security at its best.
Google Play Protect
10. Sophos Mobile Security for Android
And, finally, is a free and powerful mobile antivirus solution offered by Sophos. Apart from manual scanning of apps, its free version can scan apps automatically at set intervals too. It can also mark and show you potentially unwanted or suspicious apps you may consider uninstalling, proactively.
It has several handy features to keep your data safe and away from the prying eyes of data gobbling apps. Furthermore, it also has a built-in authenticator module, which you can use with any Google authenticator-enabled app. It can also scan and detect QR codes for any security vulnerabilities to prevent financial fraud.
Download Intercept X for Mobile for Android