Why actually you need to Safe Mode boot your android device?
Loads only the Android system apps. Eliminates all the third-party components from the start up sequence, while you can't use third party apps, you can uninstall them if any such app causes freezing your device or any problem. And also you can troubleshoot your android device.
For Jelly Bean devices:
1- Long-press the Power button until the power options menu appears.
2- Long-press the Power off option and you will be asked if you want to reboot your Android device into safe mode.
3- Press OK button
For Older Version devices:
1- Switch off your device
2- When your phone has been off, turn on the device by pressing Power button
3- While booting your phone, release Power button then press and hold volume up and down buttons together
4- The "Safe Mode" watermark will be appeared on the button left of your screen if your device has booted.
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