Anti-theft solution
Prey is an open source anti-theft solution. I decided to install it on my laptop so I could track it in case I lost it or it was stolen.
Prey is scheduled to "call home" to check the status of the device it's protecting. If it finds out the device went missing, it build a report with useful information to track down the device and tries to send it to the user. It can do the check and send the report via the Prey Control Panel (simple to setup) or you can run it in standalone mode which offers more options. I used the simple setup to find out if and how it works.
Installation
Version 0.5.3 is currently in the Debian repositories, which is easy to install (apt-get install prey) but after a few hours of trying, I couldn't get it to do anything useful: Prey noticed when my laptop was missing and created and sent the reports but they never arrived.
A post on Prey's anwers list recommended to upgrade to version 0.5.9 to get things working. I decided to install the latest version, which was 0.6.0. There's .deb for Ubuntu that I tried first on Debian Jessie/Sid, but long story short: it didn't work. Instead, I downloaded the universal .zip for Linux and made a .deb from it, the quick and dirty way.
Because it was built the quick and dirty way, Prey was complaining about a missing cronjob and configuration file.
The cronjob was in /etc/cron.d/prey when Prey expected it to be in root's list of crons. I copied the lines from /etc/cron.d/prey to crontab -e -u root and then rm'ed /etc/cron.d/prey. I changed the frequency to every 5 minutes.
Prey looked for the configuration file in /usr/lib/prey/config, which I solved by symlinking /etc/prey/config there: ln -sv /etc/prey/config /usr/lib/prey/config.
Like I said: a very quick and dirty packaging.
Configuration
To use Prey, you need to register an account. Once you've done that, log in and you will find your API key in the Account page. This key goes in your configuration file on the api_key= line. When you've set that, you can run Prey in test mode where it will check its status and generate a device key. It will immediately add the device key to the config file as well. Some moments later, your device will appear in Prey's Control Panel.
In Prey's Control Panel you can set the information you want gathered in the Devices tab. I deselected all the actions to perform on the right to keep Prey inconspicuous to a possible thief.
Testing
Set your device's status to Missing and wait for the cronjob to kick in. You should be getting a report with some very useful information a few minutes later. I checked and even when I didn't have X running, I got a nice report with a webcam picture.
Don't forget to set the status back to normal when you've verified that everything works: the free Prey account only has space for 10 reports.