Vigilo

Vigilo is a project to help my roommate and I figure out who is in the room and when. By registering a phone's bluetooth, vigilo can leverage command line tools to see who's in the room.

If you've never had a roomy in a relationship, you probably won't understand the significance of this project.

How it works

Vigilo works by using the hcitool on a Raspberry PI 3 running Ubuntu MATE. The RP3 is connected to a device (I have an iPhone) so that both trust each other. Once the RP3 trusts the (bluetooth) MAC address of the phone, it stores its name and MAC for future reference.

Once trusted, you can use the hcitool's name verb to lookup the name of a MAC address. The catch is... it only works when the device is nearby. While that might seem like a drawback, it's exactly what makes Vigilo work.

Vigilo calls hcitool name <MAC> every 30 seconds for each device. Looking up the name initiates a handshake protocol that gives away the device's name, or the empty string if the device doesn't exist. Vigilo simply feeds hcitool a list of names and parses the output. I got the guts of this from this answer on the Raspberry Pi SE site. Once you have the output, it's fairly easy to pump it into a template and ship it off.

There's one catch though when building the server: hcitool can be slow. Like really slow, sometimes taking up to 5 seconds to finish. You very well can't have an HTTP request sitting in your server for 5 seconds, even if your audience consists of two people.

To solve this, I scan using Jose Valim's answer here, on using a GenServer to store the state of the room. The state is just a list of structs with name, mac, and present fields. The GenServer uses the handle_info call to do work on its own, and then schedules itself to run 30 seconds after it finishes to start all over again. Later, the controller can access that process with call, which simply returns the state. So any user requesting the webpage isn't requesting a scan. They're requesting the state, which could be up to around 29 seconds old.

Try it yourself

Clone me (into ~ for example). Create a file for the MACs (~/vigilo/config/macs.secret.exs). Fill it with something like this:

use Mix.Config
config :vigilo, macs: ["<MAC1>", "<MAC2">, ...]

Now add this before the last line of config/config.exs:

import_config "macs.secret.exs"

And start up the server! (mix phx.server)