use strict;
use List::Util qw(reduce);

my @data = qw ( 01 b2 01 00 b6 81 81 01 b4 0a 01 01 01 01 00 
                01 00 00 01 00 c7 82 82 01 b2 01 00 b8 );

my $index;
reduce {  if ($a eq $b && $a =~ m/81|82/) {
            print "match $a starting at index $index\n"}
          $index++;
          $b;
       } @data;
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Prints:

match 81 starting at index 6
match 82 starting at index 22
[download]

Update: If you would prefer to use a for loop, you should use the range operator as below. Much cleaner to read. I guess I got carried away with the reduce.

for my $i (0 .. $#data) {
    if ( $data[$i] eq $data[$i+1] && $data[$i] =~ m/81|82/) {
        print "match $data[$i] starting at index $i\n";
    }
}
[download]