Tag Archives: location

Node-RED Geofence node

We’ve been looking at some new location based uses for Node-RED recently. To this end we’ve been standardising on adding the information under the msg.location property.

msg: {
  topic: "foo",
  payload: "bar",
  location: {
    lat: 51.02477
    lon: -1.39724

As part of this I’ve been writing a geofence node. This will allow messages to be filtered against specific regions.

The first pass worked well supporting both circular and rectangular regions, but configuring it by entering coordinates is not the most user friendly.

Screenshot from 2014-11-11 22:23:33

After a bit of playing with leafletjs and the leaflet.draw plugin I managed to come up with this which should be a lot more intuitive.

Geofence config dialog

At the moment it needs to load the leaflet js and css from a external server until we come up with a way to bundle static content inside nodes. This shouldn’t really be a problem as it’s having to load the map tiles from the internet as well. I’d like to find a way to pass in a base URL for the map server and to gracefully fall back to the text version if there is no access to a map server.

The map version also supports creating arbitrary polygon regions by joining up multiple points.

I’m still trying to get the config dialog to gracefully fall back to the basic version when there is no access to a mapserver but having problems with detecting the failure to download a map title. Any pointers would be gratefully accepted.

The code is on github and on npm. It can be installed with:

npm install node-red-node-geofence

WIFI presence detection

Back in my very first post I talked about using Bluetooth to detect my presence at home in order to disable the CCTV system and control a few other things.

While this works well it does not scale well to multiple people as the Bluetooth layer 2 ping takes about 5 seconds to time out if the device in not in range. This means that at most 12 different phones can be checked in a minute.

A couple of recent chats with a few people at work (Vaibhavi Joshi & Dale Lane and Bharat Bedi) got me thinking about this again. Modern phones tend to have WIFI as well as Bluetooth and 3G radios these days so I thought that I’d have a look at seeing if this could be used to locate devices.

After bit of a poke around it looked like a package called Kisment should be able to do what I wanted.


Kismet is a client server application, the backend server reads from the network card and decodes the packets and the UI which requests data from the server over a socket connection. This also means the backend can be on a different machine, in fact several different drone backends can be consolidated in a single master backend server and all the captured data presented to UI. This means you could distribute a number of drones over site and generate a map as devices move between areas covered by the different backends.

The default client is a ncurses based application that can list all the visible networks and a chart showing the incoming packet rates. It’s great for getting a view of what networks are active which can be very useful when you have to set up a new one and want to see which channels are free.

Rather than use the default client I decided to write my own to drive the backend the way I wanted it and to make exposing the data easier (I’m going to publish detected devices on a MQTT topic). But first I had a bit of a play using the netcat (nc) command. Netcat basically pipes stdin/stdout to and from a given socket, this is useful because the Kisment protocol is just a set of simple text commands. For example the following command will get the kismet backend to return a list of all the clients it has seen to date.

echo -e '!0 enable client MAC,manuf,signal_dbm,signal_rssi' | nc localhost 2501

Returns something that looks like this:

*CLIENT: 00:25:69:7D:53:D9 [0x01]SagemCommu[0x01] -71 0

The only tricky bit about the response is that any field that can contain a space is wrapped in characters with a value of 0x01, in this case the manufacture field could contain spaces so we need the following regexp to chop up the responses for each time a client is spotted.

I decided my client in Java (because the MQTT libraries are easy to use) so I chose to use a regular expression to split up the response

Pattern.compile("\*CLIENT: ([0-9A-F:]*) \x01(.*)\x01 (-?\d+) (\d) ");

By default Kismet cycles round all the available channels to try and get a full picture of all the WIFI traffic in range, but this means it can miss some packets and in turn miss clients that are not generating a lot of traffic. To help get round this I have locked Kismet to just listen on the same channel as my WIFI access point since all my devices are likely to try and connect to it as soon as it comes in range and there is less chance of me missing detecting my phone up front.

!1  HOPSOURCE cab63dc8-9916-11e0-b51a-0f04751ce201 LOCK 13

cab63dc8-9916-11e0-b51a-0f04751ce201 is the UUID assigned to the wifi card by kismet and the 13 is the channel I run my WIFI access point on. You can find the UUID by running the following command:

echo -e '!1234 enable source type,username,channel,uuid' | nc localhost 2501

Which returns a string that looks like this every time the back end hops to new channel.

*KISMET: 0.0.0 1308611701 [0x01]Kismet_2009[0x01] [0x01]alert[0x01] 0 
*SOURCE: orinoco_cs test 3 30b9b5a4-9b93-11e0-acfe-ee054e2c7201 
*ACK: 1234 [0x01]OK[0x01]

Publishing the last seen time on the following topic /WIFIWatch/<mac> allows applications to register to see a specific device and also build up a list of all devices ever seen and when.

WIFI Watch topics

It’s not just phones that have WIFI adapters these days, net books, tablets even digital cameras (with things like eyefi) all have , also with multiple kismet nodes it might be possible to track devices as they move around an area.

Next is to look at the signal strength information to see if I can judge a relative distance from the detection adapter.