Install Mobile Tracker on a device which should be controlled via sms messages. Then you can send control commands from any phone (if granted in app) and with any sms messenger.

Several device functionalities can be monitored and controlled like location hotspot wifi camera and many more.

With Mobile Tracker you can
• manage wifi hotspot
• manage wifi
• manage bluetooth
• manage mobile internet connection
• get battery level and check if battery is loading
• get the device's location as coordinates
• manage audio volume of all types (music ringtone ...)
• control display (manage brightness manage display off timeout and turn display off)
• take photo with default settings or custom options (flash autofocus and more)

Mobile Tracker provides flexibility with the following features.
• only grant functonalities you really need and only to phones you want
• runs in background and autostarts on boot if you want
• send multiple commands with one message
• reply to sender phone with result message (optional)
• keep an overview of all tasks like executed or failed commands

Security
Granted phones are required to be set for each module so not everyone can control the device. However if someone fakes his phone number he is able to use all enabled modules. (Note that this might be a complicated and illegal procedure. Moreover also common antitheft apps like avast trust the sender's phone number.

The app doesn't use any personal user data and permissions are only utilized for the control and monitor functionalities. The developer thanks for all productive comments.