With each new major Android version released over the past several years, Google continued to work on improving the battery life of Android-running smartphones by implementing new and improving existing battery management features. The company introduced a series of software optimizations for battery management dubbed "Project Volta" along with Android 5.0 Lollipop, and the arrival of Android 6.0 Marshmallow also marks the inclusion of "Doze": a battery-saving feature working behind the scenes whenever the smartphone's screen is turned off. However, while Doze is considered a standard feature in Android 6.0 Marshmallow, not every smartphone running the said operating system is ready for Doze, hardware-wise. In other words, although your smartphone might currently run Android 6.0 Marshmallow, Doze may or may not be active. Fortunately, there is a way to find out whether or not your handset is Doze-ready, and below you will find all the information you need to know in order to do so.
To be clear, the following method for checking if your smartphone supports Doze relies on an application that was not developed by Google, but rather a third party developer who shared the apk file on the XDA-Developers forum. With that being said, in order to install the application, you will first need to open your phone's settings menu, access "Security", and make sure that "Unknown sources" is enabled, allowing the installation of applications from unknown sources (i.e. apps from sources other than the Google Play Store, the Samsung Galaxy App store and so on). Once you've set your phone accordingly, you will need to head down to XDA-Developers (click the link) and download the attached "check_doze.apk" file on your phone. Open the file, install the application, then run it and see if your smartphone is or isn't ready for Doze. Three requirements will be shown, namely "Sensor Support", "Google Play Services Support", and "Doze Config Flag Enabled", and all three need to have a green check mark beside them in order for your phone to be compatible with Doze mode.
Assuming that your phone meets all three requirements then you're pretty much in the clear. It means that your phone already relies on Doze as long as it runs Android Marshmallow, or that your device is Doze-ready for whenever you might receive the Marshmallow update notification. Otherwise, if you're experiencing poor battery life without Doze, there's not much to do aside from manually controlling certain features on your phone in order to conserve energy, or trying one of the numerous third party battery-saving applications on the market in hopes for an alternative solution.