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HereNow - a passive location based way to put an API on a building

HereNow is a utility to add an API onto physical spaces by making educated guesses about who's in physical environment, based on whether laptops, iPads or smart phones they own are detected on networks serving the space at given moment.

Right now, the assumption here is that a space only has one wifi point, and here now only serves one network.

Why would I care?

In short, HereNow lets you do two things, which I don't see an easy way to do currently, without relying on every device having GPS tracking, and phone home to google/apple/$tech_giant each time.

It lets you:

  1. Query a number of spaces you have an existing relationship with (your office, a coworking space, your own home), to see if there's anyone in them, or crucially if people you know are there.

  2. Put an callback API onto that space, so that any kind of arbitrary GET or POST can be fired in response your or someone you know being around, without them needing to manually do this themselves (i.e. let me set an auto-checkin on foursquare when I walk into a space, or run my own set of predefined events when I enter or leave).

I'm guessing you're a developer if you're reading this, so I'm hoping I don't have to elaborate too deeply on why being able build presence based mashups is interesting.

How to install

HereNow uses node.js, and arp and nmap, two commandline tools that exist on the *nix style operating systems. You'll also need a redis server available.

On a mac:

Assuming you're using homebrew:

brew install nmap
brew install redis

On linux

Assuming you're on Debian/Ubuntu:

sudo apt-get install build-essential
sudo apt-get install nmap
sudo apt-get install redis-server
sudo apt-get install libavahi-compat-libdnssd-dev (for mdns)

To get node.js, follow the instructions at or install from source.

From there, you should be able to just use npm from within the app, to fetch all the relevant modules for javascript:

npm install

How to configure

Make copies of the example configurations in the config directory, removing 'example' from the name. Edit each one and add your own settings as appropriate.

The main settings are in config/monitor.js and are:

  • interface_name: the system name of the network interface to scan. On OSX, this will be something like en0, on Linux something like eth0.
  • nmap_delay: the time between each rescan of the network, in milliseconds.

How to run

From the app root directory:

node app.js

Navigate to http://localhost:3000 to see the web interface.

Proposed interface (WIP)

Much of the information below is proposed, and doesn't actually work yet. At the moment, you can see connected devices in the web interface and that's about it.

How to use HereNow

HereNow uses nmap and arp to populate a list of Devices, that are then matched to Owners.

When you run the Herenow app, and visit the server it will maintain a list of Owners currently in a given space, that is updated whenever someone leaves or enters, and make this list available at a given url accessible from outside the space too.

Note - you can only see the full list of devices when inside the building yourself. From the outside, you can only see the list of users.

insert picture here of list of people, and their gravatars in one group, then a collapsible list of machines, and a collapsible list of unknown devices

If you prefer to see this information over an API, you can hit the same url, but appending with the suffix /owners, to get a json array of the people listed, with a timestamp of the request made.

If you know they are in the space, you can also fetch just the json representation of that single owner, like so:

GET /owners/:username

GET /owners/:username.json

Key concepts for Herenow


You can think of anything with a network signature as being a device - an iPad, an Android phone, a laptop, or shared Printer, etc.

You might think of the json representing them like so:



You can think of an Owner as a either a Person, or a bucket for grouping devices into like "Unknown" (devices which we don't know anything about ), or "Handy shared machines" (having a shared printer on the network doesn't really signify any one person being present, but it is known).

As you get a better idea of what devices are on a network, and whose they are, the unknown bucket is likely to become smaller.

Again, if you were think of them in json, they'd like a bit like this:

  devices: (an array, keyed on their guid)

Matching devices to owners

The single most important feature of HereNow, is literally being able to see 'who is Here Now' - both from within a building, and from the outside, and then taking action based on this information.

If you're connecting to the Herenow server inside the building, you can associate devices with other owners, by POSTing, to the user resource that represents that user, with an array of uuid's of devices to associate with them. Devices can only ever belong to one owner, so POSTing a device to one owner will remove them from any others.

POST /owners/:username

POST /owners/mrchrisadams

{ uuuid }

To remove the device from the user, make a DELETE call to that nested device under the user resource.

DELETE /owners/:username/:guid

DELETE /owners/mrchrisadadams/A8e32RkfQ44eAA8e32RkfQ44eAA8e32RkfQ44eA

This has the affect of associating the device with unknown bucket once again, so it can be reassigned to someone else.

How HereNow works

There are three components that keep an upto date list of owners and devices. An nmap call fills the arp cache on a given network, with mac addresses and coresponding ip addresses. A subsequent call to arp then fetches this cache, and the main Herenow app, checks the cache against the current list of devices stored in redis, based on their mac address.

// (rubyesque pseudo code)
d = Device.findByMac;

u = User.findByDevice 

if u.exists?
 u('new device')

If new devices exist in the arp cache

a) the new device is created and the relevant details stored in redis, and a new device event is triggered

b) the device is recognised as belonging to a current owner, and status:online event is triggered for that device.


If a device no longer exists in the cache after being discovered once before:

A status:offline event is triggered for the device.

If this is the only online device associated with an owner, then that owner is removed from the current list of visible owners for the space, and an appropriate owner offline event is triggered for any browser clients that are connected.

API summary


GET owners
GET owners/:username

From within the network:

POST    owners/:username/:device_guid
GET     owners/:username/:device_guid
DELETE  owners/:username/:device_guid