Wouldn't having a wait() inside the loop make the code execute as if it wasn't forking? consider this simplified version of your script:

## simplified code, so no error checking...
foreach my $node (@devices) {
   my $pid = fork();
   if( !$pid ) {
      ## child...
      exit 0;
   }
   ## parent
   wait();
}
[download]

So this means that for each node, you fork off a process, and immediately afterwards the parent waits for that process. The parent will block until the child is done. Thus no merit of forking here...

You need to do something like this:

use POSIX;
$SIG{CHLD} = sub {
    while( ( my $pid = waitpid(-1, POSIX::WNOHANG()) ) > 0 ){
        ## cleanup code...
        ## you probably should save the forked
        ## pids and make sure that the result of
        ## waitpid is indeed your child
    }
}

foreach my $nod ( @devices ) {
   my $pid = fork();
   if( !$pid ) {
      ## child...
   }
}
[download]

Now, as for your switching needs, I might do something like this:

use POSIX;
my $do_fork = 1;
$SIG{CHLD} = sub {
    while( ( my $pid = waitpid(-1, POSIX::WNOHANG()) ) > 0 ){
        ...
    }
}

foreach my $node ( @devices ) {
    if( $do_fork ) {
        my $pid = fork();
        if( !$pid ) {
            do_exciting_things();
            exit 0;
        }
    } else {
        do_exciting_things();
    }
}
[download]

This is obviously just a psuedocode, so make sure to put plenty more error checking and all that stuff.