To clarify, $alarms = "off" is an assignment. Use == to test for numeric equality or eq to test for textual equality.

Always

use strict;
use warnings;
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Although not related to your question, you are over-using printf, which is (allegedly) slower than print. Perl, and several other languages, has interpolation - when a scalar or array variable is enclosed inside double-quotes it translates to its value. This is one of the advantages of the $ and @ prefixes. So:

printf("%s : %s\n",
        $alarmd,
        $alarms
        );
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is better written as:

print "$alarmd : $alarms\n";
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and error messages should really be routed to stderr:

print STDERR "ERROR: $error.\n";
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