The receptionist here at my office wants to know when I'm away, and I should phone or e-mail every time I leave or arrive (they're pretty low-tech, and don't mind receiving a lot of small e-mails). I tend to forget to let them know. And so does my colleague.

It was time to automate this. As I always carry a mobile phone with me, that has bluetooth enabled for my hands free car kit, I thought it would be neat to use that. Then I don't have to push any button, and can just leave, as long as I don't forget to take my phone.

I bought an extended range USB bluetooth dongle, that works perfectly under Linux. After installing bluez-utils, and compiling a kernel with a bluez stack, I wrote this script:

#!/usr/bin/perl -w
use strict;

my %phones = (
    # Bluetooth addresses
    '00:16:20:XX:XX:XX' => 'Juerd',
    'XX:XX:XX:XX:XX:XX' => 'Foo Bar',
);

{
    package Status;

    sub new {
        my ($class, $fn) = @_;
        my $self = bless {}, $class;
        open my $fh, '<', $fn or return $self;
        while (defined (my $line = readline $fh)) {
            my ($addr, $desc) = split ' ', $line, 2;
            if ($phones{$addr}) {
                $self->{ $phones{$addr} } = 1;
            }
        }
        return $self
    }

    sub present {
        my ($self, $who) = @_;
        $self->{ $who };
    }
}

package main;

use POSIX qw(strftime);

mkdir "$ENV{HOME}/.btscan" or die $! if not -e "$ENV{HOME}/.btscan";
chdir "$ENV{HOME}/.btscan" or die $!;

system 'mv now before';
system 'hcitool scan > now';

my $before = Status->new('before');
my $now    = Status->new('now');

my $time = strftime '%Y-%m-%d %H:%M:%S', localtime;

my @people = keys %{ { reverse %phones } };

for my $person (@people) {
    if ($before->present($person) and not $now->present($person)) {
        print "[$time] $person left\n";
        system './left', $person if -x 'left';
    }
    if ($now->present($person) and not $before->present($person)) {
        print "[$time] $person arrived\n";
        system './arrived', $person if -x 'arrived';
    }
}
[download]

And I ran crontab -e to let this script be run every minute:

* * * * * /root/btscan.pl
[download]

It now emailed root with concise info about my leaving and arriving. But I wanted something a little user-friendlier, so I wrote this script to send a message:

#!/usr/bin/perl -w
use strict;
use MIME::Lite;

my $to = 'foo@example.com';

my %text =
    $0 =~ /left/ ? (
        subject => "%s is weer weg",
        data    => "Dit is een geautomatiseerd bericht, dat wordt gest
+uurd " .
                   "omdat de telefoon van\n%s buiten bereik is."
    )
    :
    $0 =~ /arrived/ ? (
        subject => "%s is er weer",
        data    => "Dit is een geautomatiseerd bericht, dat wordt gest
+uurd " .
                   "omdat de telefoon van\n%s binnen bereik is."
    )
    :
    die "What am I?"
    ;

my $person = shift;

my $msg = MIME::Lite->new(
    From    => 'bar@example.org',
    To      => $to,
    Subject => sprintf($text{subject}, $person),
    Data    => sprintf($text{data}, $person),
);

$msg->send;
[download]

And symlinked that to ~/.btscan/left and ~/.btscan/arrived.

I've been using this for half a day now, and so far it has worked perfectly.

The server here can tell when I'm gone, so I no longer have to remember to notify people.

Updates:

• Removed unused time handling from mail script
• Someone told me that almost all USB bluetooth devices work under Linux because it's standardized