Script Commands - Environmental Variable not working

I'm new to MobiControl and to the scripts but having read the reference guide I don't think I'm making any rookie mistake, but please enlighten me! I'm trying to find out when a device (Samsung A6- SM-A600FN) is turned off and on, one rough way of doing this seems to be checking when a device gets switched to "User mode" (seems to always occur when a phone boots). There doesn't seem to be a built in way of alerting for this, so I thought maybe scripts would be a good place to start and then see if I can send an email alert or report from there. I can see the event in the log already but ideally I need some alert for this, as any occasion this occurs during the working day would be suspicious for us. Following the reference guide HERE and using the example code below return "%var1%" not "Hello World" as expected. set var1=Substring "Hi Hello World Goodbye" 4 11 showmessagebox %var1% Any advice would be much appreciated.