The original photo does not suggest a optosensor is being used to watch the backlight.
Yes , what I had posted its how we do it in Greece..
Its simple, low cost , and practical ..
And it called as remote activation by cell phone .. you can use it , to start the air condition , so to heat your room , before you get home .. or for another hundreds of reasons..
The young ones call it as Bomb activator , well there is hundreds of ways to do that too.
But personally I do not get excited with the name " Bomb activator " ,
for the expert ones in electronics , those are common projects and nothing more .
Ones I was had a contract to service the alarm system of one chain of super markets,
they was as 5-6 in my area .
They had also Cell phones to act in the reverse way , and do the emergency call .
So now I can say that I had do them all ... remote activation by cell phone , and the opposite .