In the last few weeks, a lot of details have been disclosed around Ross Ulbricht’s arrest. For those not familiar with the matter, Ulbricht was arrested at a library in San Francisco some time ago with his laptop open. The agents managed to steal the laptop out of Ulbricht’s hands and therefore prevent him from locking the computer (which presumably had full-disk encryption).

This got me thinking; why don’t we have Dead Man’s Switches for computers? It would be very simple to create one.

Having such device would not only be useful if you’re a high profile target (like Ulbricht), but also to conveniently lock your computer in an office environment.

Using a USB stick

Hardware

Using just things we have laying around, we should be able to design the most primitive version. All you really need is a USB stick and some strings (or lanyard)

Format your USB drive with a some random file on.

Make a bracelet out of strings or a lanyard. The string from the bracelet must be long enough such that it isn’t in the way while you’re typing/working. Imagine a modified version of this.

Software

With the hardware ready, we now need a daemon or similar that runs on your computer and checks for this file. If this file disappears (i.e. you remove the USB device), the computer will lock down.

Here’s an example of a very primitive version of such script. All it does is to check for the file every second, and if it is absent, it will lock the computer (assuming you’re using OS X):

!/bin/bash

Where is the file located?

Should be something like