Turning on a phone without using power button
If you cannot open your phone because of a broken button, here is a solution to this problem. You do not need a power button in order to turn on or wake up your phone. It does not matter if your phone or tablet is older or newer, it happens to them to break.
When the device is switched off
If your device is switched off and you do not have anymore a functional power button, you will find yourself in a difficult situation. There are some options for you, but there is no assurance that they will work properly. The first and simplest thing you can do is to plug your phone into the charger because some phone turn on by this method, but it is not likely so you may have to long press the volume buttons and hope for a boot menu to appear.
You can also try connecting the phone to a PC or laptop by using an USB. It should boot up instantly.
A third option is strictly linked with an enabled USB debugging. So, if you had enabled this after the phone switched off, you can use a command prompt. Install ADB and launch a command prompt window. Plug your phone to your computer and type `adb reboot`.
When the device is switched on
If you find yourself among those lucky ones that have a device that is still switched on and the power button is broken, things will be easier for you. The first thing you should do is make sure your phone or tablet does not run out of power.
Some phones like Samsung Galaxys and iPhones do not encounter too much trouble with a broken power button. They have a physical home button below the screen that will wake up the phone. Anyway, other smartphone nowadays do not have that kind of button which will make things trickier when it comes to waking up without the power button.
There are many things you can do in order to wake up your phone. You can put it to charge or you can put someone to call you. This will wake up your screen. You can try ( if you have) using the physical camera button which will start the camera app.
Those are not convenient ways of waking up your phone, so after managing doing so, you should install some apps that will provide you access without a power button. Also, you have to keep in mind the fact that you do not have to let him run out of power. In that case, the things will get more troublesome.
A gravity screen will make your phone sleep when is set face down on a flat surface or in your pocket. It will wake it up when you move it. You can use Proximity Actions for this through the Shake Screen On/Off method, which is pretty simple to use.