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.

Not working anymore in new openwrt versions, due to "ujail" limitations.
See openwrt/openwrt#9856

Now you must put script in /etc/hotplug.d/dhcp (as "00-detect_new_device.sh") and you must rewrite conditions to use environment variables ACTIONS(='add'), IPADDR, MACADDR, HOSTNAME.
See an example here:
https://forum.openwrt.org/t/how-to-detect-dhcp-assignment-to-send-an-email-on-openwrt/24416/2

Anyone have a updated script?

I modfied that awesome script and it now works for me with the latest openwrt release. Just put that file into the directory "/etc/hotplug.d/dhcp".
I named it 99-detect_new_device.sh

here it is:

#!/bin/sh
# script to detect new dhcp lease

#saved mac addresses to just notice new unknown devices
known_mac_addr="/etc/known_mac_addr"
#set here your email address
notification_email="**youremailaddress**"

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

if [ "$ACTION" = add ] && [ "$unknown_mac_addr" -ne 0 ]; then
    (
        echo "Subject: new DHCP lease on $(hostname)"
        echo ""
        echo "A new DHCP lease has been assigned: MAC=$MACADDR, IP=$IPADDR, NAME=$HOSTNAME"
    ) | sendmail "$notification_email"
fi

I modified the original version to customize the emails based on the network which the assigned IP address belongs to (Lan, IoT, Guest).

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

known_mac_addr="/etc/config/dhcp"
notification_email="xxx@gmail.com"
lan="192.168.x."       #Update subnets for the lan, guest, iot
guest="192.168.y."
iot="192.168.z."

#Convert MAC to uppercase
mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

if [ "$ACTION" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $ACTION $mac $IPADDR $HOSTNAME"

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
    echo `date` "LAN" $msg >> /tmp/dhcpmasq.log
    echo "LAN" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
    echo `date` "Guest" $msg >> /tmp/dhcpmasq.log
    echo "Guest" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
    echo `date` "IoT" $msg >> /tmp/dhcpmasq.log
    echo "IoT" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

fi

I modified the original version to customize the emails based on the network which the assigned IP address belongs to (Lan, IoT, Guest).

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

known_mac_addr="/etc/config/dhcp"
notification_email="xxx@gmail.com"
lan="192.168.x."       #Update subnets for the lan, guest, iot
guest="192.168.y."
iot="192.168.z."

#Convert MAC to uppercase
mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

if [ "$ACTION" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $ACTION $mac $IPADDR $HOSTNAME"

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
    echo `date` "LAN" $msg >> /tmp/dhcpmasq.log
    echo "LAN" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
    echo `date` "Guest" $msg >> /tmp/dhcpmasq.log
    echo "Guest" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
    echo `date` "IoT" $msg >> /tmp/dhcpmasq.log
    echo "IoT" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

fi

Awesome!
Does ist work with openWRT 22.03.5?

I modified the original version to customize the emails based on the network which the assigned IP address belongs to (Lan, IoT, Guest).

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

known_mac_addr="/etc/config/dhcp"
notification_email="xxx@gmail.com"
lan="192.168.x."       #Update subnets for the lan, guest, iot
guest="192.168.y."
iot="192.168.z."

#Convert MAC to uppercase
mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

if [ "$ACTION" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $ACTION $mac $IPADDR $HOSTNAME"

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
    echo `date` "LAN" $msg >> /tmp/dhcpmasq.log
    echo "LAN" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
    echo `date` "Guest" $msg >> /tmp/dhcpmasq.log
    echo "Guest" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
    echo `date` "IoT" $msg >> /tmp/dhcpmasq.log
    echo "IoT" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

fi

Awesome! Does ist work with openWRT 22.03.5?

I’m on 22.03.2, should work on 22.03.5 as well.

I modified the original version to customize the emails based on the network which the assigned IP address belongs to (Lan, IoT, Guest).

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

known_mac_addr="/etc/config/dhcp"
notification_email="xxx@gmail.com"
lan="192.168.x."       #Update subnets for the lan, guest, iot
guest="192.168.y."
iot="192.168.z."

#Convert MAC to uppercase
mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

if [ "$ACTION" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $ACTION $mac $IPADDR $HOSTNAME"

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
    echo `date` "LAN" $msg >> /tmp/dhcpmasq.log
    echo "LAN" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
    echo `date` "Guest" $msg >> /tmp/dhcpmasq.log
    echo "Guest" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
    echo `date` "IoT" $msg >> /tmp/dhcpmasq.log
    echo "IoT" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

fi

Awesome! Does ist work with openWRT 22.03.5?

I’m on 22.03.2, should work on 22.03.5 as well.

so now mailsend is installed and works just fine.
Unfortunately your script does not work. I got in to my wifi with my smartphone (random mac setting is on) but there is nothing happening.

I modified the original version to customize the emails based on the network which the assigned IP address belongs to (Lan, IoT, Guest).

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

known_mac_addr="/etc/config/dhcp"
notification_email="xxx@gmail.com"
lan="192.168.x."       #Update subnets for the lan, guest, iot
guest="192.168.y."
iot="192.168.z."

#Convert MAC to uppercase
mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

if [ "$ACTION" == "add" ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on `uci get system.@system[0].hostname`.`uci get dhcp.@dnsmasq[0].domain` $ACTION $mac $IPADDR $HOSTNAME"

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
    echo `date` "LAN" $msg >> /tmp/dhcpmasq.log
    echo "LAN" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
    echo `date` "Guest" $msg >> /tmp/dhcpmasq.log
    echo "Guest" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
    echo `date` "IoT" $msg >> /tmp/dhcpmasq.log
    echo "IoT" $msg | mailsend -smtp smtp.gmail.com -port 465 -t $notification_email -f root@openwrt -ssl -auth -sub "OpenWRT New LAN Device Connected" -user xxx@gmail.com -pass "password"
  fi

fi

Awesome! Does ist work with openWRT 22.03.5?

I’m on 22.03.2, should work on 22.03.5 as well.

so now mailsend is installed and works just fine. Unfortunately your script does not work. I got in to my wifi with my smartphone (random mac setting is on) but there is nothing happening.

Typically, the random MAC addresses don't change on every connection attempt, so it's possible that the MAC address was already assigned a dynamic IP address and doesn't request a new IP address to be assigned. If this is the case, a new email won't be generated till the IP lease is expired. You can check to see when the IP assignment will expire from the Status page, listed under "Lease time remaining". Quickest way to discard the assignment/lease, would be to reboot your router and attempt to connect to it again.

In addition to the email, there should be an entry created in /tmp/dhcpmasq.log. You can check this file to verify as well, incase the issue is related to email setup.

@EnlightedBitFox, also confirming you did update the following:

• The mailsend commands with your credentials.
• notification_email="xxx@gmail.com"
• lan="192.168.x." #Update subnets for the lan, guest, iot
• guest="192.168.y."
• iot="192.168.z."

I checked both, the mac and the file.
The mac does change everytime when a connection is established. About the dhcpmasq.log, there isnt one.

@EnlightedBitFox, also confirming you did update the following:

• The mailsend commands with your credentials.
• notification_email="xxx@gmail.com"
• lan="192.168.x." #Update subnets for the lan, guest, iot
• guest="192.168.y."
• iot="192.168.z."

Yes is did. I changed the ips matching mine. I doesnt have a subnet for guest and iot

@EnlightedBitFox, also confirming you did update the following:

• The mailsend commands with your credentials.
• notification_email="xxx@gmail.com"
• lan="192.168.x." #Update subnets for the lan, guest, iot
• guest="192.168.y."
• iot="192.168.z."

Yes is did. I changed the ips matching mine. I doesnt have a subnet for guest and iot

Can you try removing the # in front of the following line ~11. So that it starts with echo.
#echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

After doing so, connect a device with a new MAC address and see if you get anything in the /tmp/detect file.

@EnlightedBitFox, also confirming you did update the following:

• The mailsend commands with your credentials.
• notification_email="xxx@gmail.com"
• lan="192.168.x." #Update subnets for the lan, guest, iot
• guest="192.168.y."
• iot="192.168.z."

Yes is did. I changed the ips matching mine. I doesnt have a subnet for guest and iot

Can you try removing the # in front of the following line ~11. So that it starts with echo. #echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect

After doing so, connect a device with a new MAC address and see if you get anything in the /tmp/detect file.

About the subnets:
Do i have to enter the subnet-ID or just the 3. octet?

@EnlightedBitFox, also confirming you did update the following:

• The mailsend commands with your credentials.
• notification_email="xxx@gmail.com"
• lan="192.168.x." #Update subnets for the lan, guest, iot
• guest="192.168.y."
• iot="192.168.z."

Yes is did. I changed the ips matching mine. I doesnt have a subnet for guest and iot

Can you try removing the # in front of the following line ~11. So that it starts with echo. #echo $ACTION $MACADDR $IPADDR $HOSTNAME >>/tmp/detect
After doing so, connect a device with a new MAC address and see if you get anything in the /tmp/detect file.

About the subnets: Do i have to enter the subnet-ID or just the 3. octet?

Just the 3, since you're looking for a text pattern.

Uncommenting the lined mentioned earlier by removing the #, will post an entry in the /tmp/detect file upon the script being run, that will rule out any potential filtering issues.

Additionally, did you also follow the steps from the 1st post from the original author. Those steps are required to call this script.

Hello,
I checked the system log and I found the following:
Thu May 11 06:26:22 2023 daemon.err dnsmasq[1]: failed to execute /etc/detect_new_device.sh: No such file or directory.
TBH i dont understand why. I placed the detect_new_device.sh script in /etc/

I checked mine and at some point I moved it to the following location and changed the name:
/etc/hotplug.d/dhcp/00-detect_new_device.sh

Don't recall why, but must have been due to an issue that came up, possibility with v22.xx.x

Also change the file permissions to make it executable using:
chmod +x /etc/hotplug.d/dhcp/00-detect_new_device.sh

Ahh ok will try it out.
You changed it, because on the ujail permissions.
What about the dnsmasq.conf? I assume, the only thing to do is adjusting the path

Yes, its coming back to me :)

Actually the dnsmasq.conf file no longer has the entry, I have it commented out.

Awesome!
Now it works 😁
Thank you ✌️

I upgrade my openwrt to 23, the dhcp script breaks. I figure it out and finally make it works again. Share my procedure to help others.

This is my dhcp script:

#!/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
#echo "$0" "My custom script called with $@"
#echo "$1 $2 $3 $4"
known_mac_addr="/etc/config/dhcp"

send_notification(){
    msg="$1"
    curl "https://<myhookapi>/WLAN_NEW_CLIENT_ALERT! $msg"
}

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

if [ "$ACTION" = add ] && [ "$unknown_mac_addr" -ne 0 ]; then
  msg="New device on $(uci get system.@system[0].hostname).$(uci get dhcp.@dnsmasq[0].domain) MAC=$2, IP=$3, NAME=$4"
  echo "$msg"

  send_notification "$3_$4"

fi

After I add it to config with uci set, the openwrt log shows:

...
grep: /etc/config/dhcp: No such file or directory
...
line 24: /bin/grep: not found

There are much logs like that. So I check the dnsmasq service script, thinking maybe the ujail restrict the command and file access, and the I modify the /etc/init.d/dnsmasq file.

DHCPSCRIPT="/usr/lib/dnsmasq/dhcp-script.sh"
DHCPSCRIPT_DEPENDS="/usr/share/libubox/jshn.sh /usr/bin/jshn /bin/ubus /bin/grep /usr/bin/curl /etc/config/dhcp"

I update the DHCPSCRIPT_DEPENDS to add the command and file needed in dhcp script. After that, everything works, and error log has gone.

It's a little nasty, if someone knows there is a more elegant way to change the DHCPSCRIPT_DEPENDS, please share.

I extended it a bit to send tmessaged through a telegram bot

My script:

#!/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

# logger -p local0.info -t dhcp-join-notify "$0: My custom script called with $@"

known_mac_addr="/etc/config/dhcp"


BOT_TOKEN='<INSERT_TOKEN_HERE>'
CHAT_ID='<INSERT_GROUP_CHAT_ID>'


send_notification(){
    msg="$1"
    curl -ks https://api.telegram.org/bot$BOT_TOKEN/sendMessage -d chat_id=$CHAT_ID -d parse_mode=HTML -d text="$msg" >/dev/null
}
# check if the mac is in known devices list
/bin/grep -iq "$2" "$known_mac_addr"
unknown_mac_addr=$?

if [ "$1" = add ] && [ "$unknown_mac_addr" -ne 0 ]; then
  local_msg="New device detected: MAC=$2, IP=$3, NAME=$4"
msg="New device joined the home network:
Hostname: <b>$4</b>
IP Address: <b>$3</b>
MAC Address: <b>$2</b>"
  logger -p local0.info -t dhcp-join-notify "$local_msg"

  send_notification "$msg"

fi

The init script change:
DHCPSCRIPT_DEPENDS="/usr/share/libubox/jshn.sh /usr/bin/jshn /bin/ubus /bin/grep /usr/bin/curl /etc/config/dhcp /usr/bin/logger /sbin/uci /etc/ssl/certs/ca-certificates.crt"

I did not use /etc/hotplug... but installed the script through something like uci set dhcp.@dnsmasq[0].dhcpscript='/root/alert_dhcp_new_device.sh'

I extended it a bit to send tmessaged through a telegram bot

My script:

#!/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

# logger -p local0.info -t dhcp-join-notify "$0: My custom script called with $@"

known_mac_addr="/etc/config/dhcp"


BOT_TOKEN='<INSERT_TOKEN_HERE>'
CHAT_ID='<INSERT_GROUP_CHAT_ID>'


send_notification(){
    msg="$1"
    curl -ks https://api.telegram.org/bot$BOT_TOKEN/sendMessage -d chat_id=$CHAT_ID -d parse_mode=HTML -d text="$msg" >/dev/null
}
# check if the mac is in known devices list
/bin/grep -iq "$2" "$known_mac_addr"
unknown_mac_addr=$?

if [ "$1" = add ] && [ "$unknown_mac_addr" -ne 0 ]; then
  local_msg="New device detected: MAC=$2, IP=$3, NAME=$4"
msg="New device joined the home network:
Hostname: <b>$4</b>
IP Address: <b>$3</b>
MAC Address: <b>$2</b>"
  logger -p local0.info -t dhcp-join-notify "$local_msg"

  send_notification "$msg"

fi

The init script change: DHCPSCRIPT_DEPENDS="/usr/share/libubox/jshn.sh /usr/bin/jshn /bin/ubus /bin/grep /usr/bin/curl /etc/config/dhcp /usr/bin/logger /sbin/uci /etc/ssl/certs/ca-certificates.crt"

I did not use /etc/hotplug... but installed the script through something like uci set dhcp.@dnsmasq[0].dhcpscript='/root/alert_dhcp_new_device.sh'

Do you have a script for when someone is disconnected from your wifi ? I've been trying to figure out how to do that, currently I only have a script that tells me when a new device is connected to wifi but not when it's disconnected

This is my variation that script (etc\hotplug.d\dhcp\99-detect_new_device_email.sh ).
I have Lan, Guest and IoT.
Router send me an alert when someone connect/disconnect. (lease time run out).
I disabled known/unknown hosts

#!/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 = $ACTION = add | update
# $2 = $MACADDR = mac address
# $3 = $IPADDR = ip address
# $4 = $HOSTNAME = device name

# this will create log file 
echo "$ACTION     $HOSTNAME     $IPADDR     $MACADDR      `date`">>/tmp/detect.log

known_mac_addr="/etc/config/dhcp"
notification_email="YOUR_Email@gmail.com"
lan="192.168.2."       #Update subnets for the lan, guest, iot
guest="192.168.4."
iot="192.168.3."

# Convert MAC to uppercase if you want
# mac=$(echo "$MACADDR" | awk '{print toupper($0)}')

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

# && [ "$unknown_mac_addr" -ne 1 ]

if [ "$ACTION" == "add" ]; then

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Connected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "LAN") | sendmail "$notification_email"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Connected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "Guest") | sendmail "$notification_email"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Connected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "IoT") | sendmail "$notification_email"
  fi
fi
if [ "$ACTION" == "remove" ]; then

  if test "${IPADDR#*$lan}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Disconnected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "LAN") | sendmail "$notification_email"
  fi

  if test "${IPADDR#*$guest}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Disconnected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "Guest") | sendmail "$notification_email"
  fi

  if test "${IPADDR#*$iot}" != "$IPADDR"; then
      ( echo "Subject: $HOSTNAME    Disconnected"
        echo ""
        echo "NAME:  $HOSTNAME"
        echo ""
        echo "MAC:   $(echo "$MACADDR" | awk '{print toupper($0)}')"
        echo "IP:   $IPADDR" 
        echo ""
        echo "IoT") | sendmail "$notification_email"
  fi
fi

"$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

"$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).

"$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

"$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.