Device on/off network sensing program

Need program written that will look for specified devices on local wireless networks and once device(s) is/are found the program will send a predetermined string out a specified com port. For example, if Iphone X is currently OFF network and then is found ON network, send RS232 "x" string out thru com port 4. If same device is currently ON network, then is determined that it is no longer ON network, send RS232 "y" string out thru com port 4. This program needs to be able to allow us to specify the devices possibly using Mac address and also specify the strings for that device when logging on and off the network. Needs to run on a Windows OS Would like to add features of project requested. I would like the program to be able to send a email to a predetermined email address(s) with a preset content (body of email) when a predetermined string is received on same serial port as first part of program. I would need a admin area with the ability to enter string to be received, content, email address(s) to be sent to. Also a note field attached to string for in house notes regarding string. I would like a character counter for content to be sent as info may be sent as text message.