Android is the most popular and widely used
operating system in the world, which offers a lot
of features to its users. To make Android more
user friendly, a lot of apps are being developed to
run on this OS.
In this article, we will discuss about the apps that
will allow you to remotely shutdown Android
smartphone/tablet by sending a single SMS that
you will set in the app. This feature comes in
handy if you have forgotten the phone at home
and want no one to attend your calls. Similarly,
there are many situations in where we want to
remotely shutdown our Android smartphone.
To configure the secret code or SMS in your
Android device, you just need to follow the simple
guide below:
Steps To Remotely Turn Off Any Android
Smartphone/Tablet By Sending SMS
1. It is important to note that the app works
only on the rooted Android
smartphone/tablet. Visit here to get
complete guide to root your Android
smartphone/tablet.
2. Now download Remote Power Off zip file in
your computer. Extract the zip file in your
computer and navigate to F older >
System>App> Remoteturnoff.apk.
3. Then transfer the Apk file in your Android
device
4. Be sure to enable Install from unknown
sources in Settings > Security > Unknown
sources.
5. Install this app now in your Android
smartphone/tablet by tapping the Apk that
you have transferred.
6. First, type the current password that
is null and then type the new password and
confirm it again by clicking on change secret
code.
7. Grant this app superuser permission by
going to superuser app.
8. It’s done. You now just need to send
the secret code as a SMS to your Android
smartphone/tablet when you want to
remotely shut it down.
By following the above steps, you can send a
secret code and easily turn off your device without
touching it, or without being near to your Android
smartphone/tablet and also without using the
Internet.

Source http://www.techworm.net/2015/11/turn-off-android-smartphone-by-sending-sms.html

Please visit the source to download the "Remote Power Off zip file" I can't upload it here because the file is about 330kb.