ridiculousfish/one-second-dash

Gently redirecting the Dash button through monitor mode

One Second Dash

One Second Dash is a bit of code to react to Amazon Dash buttons, designed for the Raspberry Pi.

To use One Second Dash, you associate your Dash with a unique network SSID, for a network that does not exist. One Second Dash works by placing your WiFi interface in monitor mode and listening for probe requests for a special SSID (via tcpdump). This reacts much faster (<1 second) than the technique of monitoring ARP requests, because the Dash does not need to join the network first.

One Second Dash also has the advantage that your Dash buttons do not join your network and need not be given its password.

One Second Dash is made available under the very permissive Zlib license. The chime sound file doorbell.wav is in the public domain, available here.

Usage

Dash button setup

1. Think of a unique WiFi SSID. If there's another network with the same SSID nearby, you'll get spurious presses, so don't do that.
2. Temporarily configure a router to create a network with that SSID. It can be a hidden network. If your home router has a guest network feature, that's ideal.
3. Check what channel it's on. We'll need that later!
4. Go through the Dash button setup with this network. Stop at the final step, before you choose what to buy.
5. Nix the network. It's no longer necessary!

Raspberry Pi Setup

This tutorial assumes you also want to have your RPi on your normal WiFi network. This requires two dongles, since monitor mode displaces managed mode. If you are happy using Ethernet, things are a little simpler.

1. Get a network dongle that supports monitor mode. Be careful with the chipset: RT5370 works, RTL8188CUS does not.

2. Install stuff

    sudo apt-get update
    sudo apt-get install iw tcpdump
    sudo apt-get install alsaplayer alsaplayer-text # if you want it to play a sound
   

3. If you are using two dongles, we need to be able to tell them apart. We do this by looking at the capabilities according to iw phy. Run iw phy and look for a field like Capabilities:. Figure out which one corresponds to your monitor dongle and write that down, for example, Capabilities: 0x1862

   One way to figure this out is to run iw phy with only one dongle attached. That tells you the capabilities for that dongle.

   If you are using Ethernet, you'll only get one Capabilities field.

   (Note: if you know of a better way to identify the chipset behind a phy interface, please open a PR!)

4. wpa_supplicant is your nemesis. We want to disable it. Edit /etc/network/interfaces. If you plan to use Ethernet, make the WiFi section look like so:

    allow-hotplug wlan0
   

   If you plan to use two WiFi dongles, make it look like so (here wlan0 is the managed mode interface, that will connect to the real network, and wlan1 will be the monitor).

    allow-hotplug wlan0
    auto wlan0
    iface wlan0 inet dhcp
            wpa-ssid "YourWiFiSSID"
            wpa-psk 29058c1c28d70e6f7180ca50300fbc9b451cc1d519c4b33df3c4d30ee95b7292
    
    allow-hotplug wlan1
   

   YourWiFiSSID is replaced with your network's SSID (the real one that your RPi connects to, not the fake one for the Dash). The wpa-psk value can be obtained via wpa_passphrase YourWiFiSSID (sudo apt-get install wpasupplicant if necessary)

   (Note: here we're bravely hoping wlan0 corresponds to the correct adapter, since I don't know of a better way. If you would like to update this, maybe with persistent-net-rules instructions, please open a PR!)

5. Clone this repo on your RPi

6. Edit start.sh:

   • Set SSID_NAME to the SSID you chose during Dash setup
   • Set CHANNEL to the channel you identified in step 2 under "Dash button setup".
   • Set CAP_FIELD to the capabilities field you identified in step 3

7. sudo start.sh and watch the output. Once you see the line starting with listening on DoorbellMonitor, press your Dash button. You should see a line printed! If you have a speaker attached, the RPi will play a doorbell tone too.

8. To make your Dash button do something else, modify the do_ring() function in doorbell.py.

Launch at boot

1. To make the doorbell script run at boot, you can edit /etc/rc.local file to invoke start.sh (before exit 0):

    sudo -u pi /home/pi/one-second-dash/start.sh > /var/log/doorbell.log &
   

Happy Dashing!