A broken power button does not have to mean it's the end for a phone or tablet. Here are some tips to try that will help you turn on your phone without the power button - and to continue using it as normal.
If your phone is still turned on:
Do NOT let it switch off. Keep it charged, carry a power bank, and if you need to reboot make sure you select that option rather than power off.
Install some apps that can help. Power Button to Volume Button lets you use your volume button instead of the power button. Gravity Screen wakes your phone screen when you pick up the device, and Shake Screen On Off does something similar. Proximity Actions can wake the screen by gesturing to the proximity sensor.
Set an alarm to go off at a specific time every day: this will trigger some phones to switch on in order to sound the alarm. Maybe set a few alarms, just in case.
If you're worried about waking the screen without the power button, look in the settings for any options to wake the screen via alternative methods. For example, turn on double-tap to wake, and if your phone has a pressure-sensitive virtual home button make sure it is enabled. Some phones will also let you use the volume or camera keys to wake the screen. If all else fails, get someone to ring you and access the phone that way.
For reasons we will outline below you should also turn on USB debugging, and download and install Minimal ADB & Fastboot on a computer. Open Settings, About Phone, Software Information, and tap Build number seven times. Now go to Settings, Developer Options, and turn on USB debugging.
Plug the phone into your computer via USB, and select the option that pops up on your phone to allow USB debugging. If there is an option to 'Always allow on this computer' make sure it is selected.
If your phone is turned off:
Try the easy solution first: if your phone ran out of battery then plug it into a charger and see if it will turn on by itself. You may need to wait a few minutes if the battery is completely dead.
Sometimes plugging it into a charger won't force a device to turn on, but plugging it into a computer's USB port can do so - try that too.
If you followed our advice above and set an alarm, you can also wait for this to go off - ensure your battery is sufficiently charged before that time comes.
Another option is to turn on the phone via the recovery menu, although most phones require you to use the power button to access this, and often to select options within. If your phone accesses the recovery menu by some other combination of the home and volume keys that does not involve the power button, you'll be in luck. Google your phone model and 'recovery menu' to find out.
If you enabled USB debugging and installed Minimal ADB & Fastboot before the phone turned off, go to your computer and launch the tool. Plug in your phone via USB, then type adb reboot and hit enter. Also try adb reboot recovery. This will not work for all phones when they are switched off, but it is worth a try.