Detect new network devices connecting to OpenWrt and send text message

OpenWrt detect new device and send text message.md

Add the following line in /etc/dnsmasq.conf

dhcp-script=/etc/detect_new_device.sh

Setup sendmail to send email to your text number.

Reference:

• https://wiki.openwrt.org/doc/howto/smtp.client
• https://fixmynix.com/send-mail-command-line-linux-openwrt/
• http://lifehacker.com/5506326/how-can-i-send-an-email-via-text-message

Create /etc/detect_new_device.sh with the following content

#!/bin/sh

# script to detect new dhcp lease

# this will be called by dnsmasq everytime a new device is connected
# with the following arguments
# $1 = add | old
# $2 = mac address
# $3 = ip address
# $4 = device name

notification_email="1234567890@txt.att.net"

if [ "$1" == "add" ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $*"
  echo `date` $msg >> /tmp/dhcpmasq.log

  # encode colon (:) and send email
  echo $msg | sed s/:/-/g | sendmail "$notification_email"
fi

Alternative script using whitelist

This script only sends alerts if the mac address is not in the list

#!/bin/sh

# script to detect new dhcp lease

# this will be called by dnsmasq everytime a new device is connected
# with the following arguments
# $1 = add | old
# $2 = mac address
# $3 = ip address
# $4 = device name

known_mac_addr="/etc/known_mac_addr"
notification_email="1234567890@txt.att.net"

# check if the mac is in known devices list
grep -q "$2" "$known_mac_addr"
unknown_mac_addr=$?

if [ "$1" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $*"
  echo `date` $msg >> /tmp/dhcpmasq.log

  # encode colon (:) and send email
  echo $msg | sed s/:/-/g | sendmail "$notification_email"
fi

When a new device is added, dnsmasq calls detect_new_device.sh with arguments add mac_addr ip_addr devicename. The script checks if the device is new (if the dhcp lease hasn't expired, it calls with old), then logs and emails (which eventually is a text message) the information.

"$ACTION" == "remove"

This action doesn't work when someone's device disconnects from a wifi network, I have a workaround by pinging their device IP every minute and send me a notification when the ping fails but it's not very reliable, sometimes the ping fails when their device is still connected to my wifi

You have to wait til DHCP lease time run out. Set up lease time shorter. I have 30m (=30 minutes). Check out log file (/tmp/detect.log).

Correct me if I'm wrong here, if you set the lease time of 30 minutes doesn't that mean "$ACTION" == "remove" will always be triggered every 30 minutes ? And that doesn't even mean that a device is disconnected from wifi

Yes, Every 30 minutes will try DHCP add new lease or Update or remove lease. But you can specify every host own lease time or general lease time reduce to 2m (2 minutes).

I tried to use hostapd, but it was not ideal:

1. lots of connections and disconections when signal is not perfect everywhere
2. missing host IP in hostapd

If somebody have better soution please share it.