Geez. One can only hope that this "emergency message" doesn't mean something like "reactor coolant low"!

To make this into a single process, you will need to determine whether or not the socket for the device has a line for you to process in it or not. I think that you will need IO::Socket. This sort of thing would be done in what is called a "select server". Don't read from the socket unless you know that it has something to say.

I think this psuedo code would be fine in your application.

# open file handles for reading and reporting
# set $since_report_secs (seconds) = 0

while (sleep (1))
{
   my $emergency = check_for_emergency();
   if ($emergency)
   {
      do something; 
   }
   
   report_awake_status();
}


sub check_for_emergency
{
   while (device port ready to read)
   {
      read line and check it for "emergency"
      return 1 if emergency;
   }
   return 0; # "no error"; 
}

sub report_awake_status 
{
    $last_report_time++;
    if (more than 30 minutes)
    {
       send awake message, set counter back to zero
    }
}
[download]

The above code essentially sets up a "polling loop". This is not as efficient as it "could be". But the logic for a simple single process is simple and I think that you will find that code like this doesn't take much CPU time.