monitor

TL;DR: Passive Bluetooth presence detection of beacons, cell phones, and other Bluetooth devices. Useful for mqtt-based home automation, especially when the script runs on multiple devices, distributed throughout a property.

Frequently Asked Questions

Installation Instructions

Set Up Raspberry Pi From Scratch

Installation Instructions for Raspberry Pi Zero W

Setup of SD Card

1. Download latest version of raspbian here

2. Download etcher from etcher.io

3. Image raspbian lite stretch to SD card. Instructions here.

4. Mount boot partition of imaged SD card (unplug it and plug it back in)

5. To enable ssh, create blank file, without any extension, in the root directory called ssh

6. To setup Wi-Fi, create wpa_supplicant.conf file in root directory and add Wi-Fi details for home Wi-Fi:

country=US
    ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
    update_config=1

network={
    ssid="Your Network Name"
    psk="Your Network Password"
    key_mgmt=WPA-PSK
}

7. On the first startup, insert SD card and power on Raspberry Pi Zero W. On first boot, the newly-created wpa_supplicant.conf file and ssh will be moved to appropriate directories. Find the IP address of the Pi via your router.

Configuration and Setup

1. SSH into the Raspberry Pi (default password: raspberry):

ssh pi@theipaddress

2. Change the default password:

sudo passwd pi

3. Update and upgrade:

sudo apt-get update
sudo apt-get upgrade -y
sudo apt-get dist-upgrade -y
sudo reboot

5. Install Bluetooth Firmware, if necessary:

#install Bluetooth drivers for Pi Zero W
sudo apt-get install pi-bluetooth

6. Reboot:

sudo reboot

7. Install Mosquitto 1.5+ (important step!):

# get repo key
wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key

#add repo
sudo apt-key add mosquitto-repo.gpg.key

#download appropriate lists file 
cd /etc/apt/sources.list.d/
sudo wget http://repo.mosquitto.org/debian/mosquitto-stretch.list

#update caches and install 
apt-cache search mosquitto
sudo apt-get update
sudo apt-get install -f libmosquitto-dev mosquitto mosquitto-clients libmosquitto1

Monitor Setup

Setup monitor

1. Clone monitor git:

#install git
cd ~
sudo apt-get install git

#clone this repo
git clone git://github.com/andrewjfreyer/monitor

#enter `monitor` directory
cd monitor/

#(optional) switch to beta branch for latest updates and features (may be unstable)
git checkout beta       

2. Initial run:

Configuration files will be created with default preferences. Any executables that are not installed will be reported. All can be installed via apt-get install ...

sudo bash monitor.sh

3. Edit mqtt_preferences file:

sudo nano mqtt_preferences

4. Edit known_static_addresses (phones, laptops, some smart watches):

sudo nano known_static_addresses

Alternatively, send an mqtt message to monitor/setup/ADD STATIC DEVICE with a message including a mac address and an alias separated by a space:

topic: monitor/setup/ADD STATIC DEVICE message: 00:11:22:33:44:55 alias

Use, monitor/setup/DELETE STATIC DEVICE with a message containing a mac address to remove a device from all monitor nodes.

5. Read helpfile:

sudo bash monitor.sh -h

Now the basic setup is complete. Your broker should be receiving messages and the monitor service will restart each time the Raspberry Pi boots. As currently configured, you should run sudo bash monitor.sh a few times from your command line to get a sense of how the script works.

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Background & Technical Details

Highlights

monitor sends a JSON-formatted MQTT message including a confidence value from 0 to 100 to a specified broker when a specified Bluetooth device responds to a name query. By default, name queries are triggered after receiving an anonymous advertisement from a previously-unseen device (e.g., a device in peripheral mode advertising an ability to connect).

Example JSON package:

topic: monitor/{{name of monitor install}}/{{mac address}}
message: {
    "id":"{{mac address}}",
    "confidence":"{{ranging from 0-100}}",
    "name":"{{if available}}",
    "manufacturer":{{if available}}",
    "type":"KNOWN_MAC",
    "retained":"{{message retained?}}",
    "timestamp":"{{formatted date at which message is sent}}",
    "version":"{{monitor version}}"
 }

In addition, optionally, a JSON-formatted MQTT message can be reported to the same broker whenever a publicly-advertising beacon device or an iBeacon device advertises.

Example JSON package:

topic: monitor/{{name of monitor install}}/{{mac address or ibeacon uuid}}
message: {
    "id":"{{mac address or ibeacon uuid}}",
    "report_delay":"{{delay from first detection to this message in seconds}}",
    "flags":"{{GAP flags}}",
    "movement":"stationary",
    "confidence":"{{ranging from 0-100}}",
    "name":"{{if available}}",
    "power":"{{if available}}",
    "rssi":"{{if available}}",
    "mac":"{{if ibeacon, the current mac address associated with the uuid}}",
    "manufacturer":{{if available}}",
    "type":"{{GENERIC_BEACON_PUBLIC or APPLE_IBEACON}},
    "retained":"{{message retained?}}",
    "timestamp":"{{formatted date at which message is sent}}",
    "version":"{{monitor version}}"
 }

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Oversimplified Analogy of the Bluetooth Presence Problem

Imagine you're blindfolded in a large room with other people. We want to find out who of your friends is present and who of your friends isn't present:

Some of the people in the room periodically make sounds (e.g., eating a chip, sneeze, cough, etc.), others sit quietly and don’t make a sound unless you specifically ask for them by name, and still others periodically announce their own name out loud at regular intervals whether or not you want them to do that:

Here's the problem. You can’t just shout “WHO’S HERE” because then everyone would say their name at the same time and you couldn’t tell anything apart. Similarly, for obvious reasons, you can't simply ask "WHO ISN'T HERE?"

So, you take attendance like in a classroom. Everyone in the room responds only when their own name is shouted.

So, one way to take attendance is to shout for each friend on a list by name, one at a time, repeatedly. Ask for someone, get a response, wait for a moment, and ask again.

Once a friend stops responding (for some period of time), you presume that he or she has left:

This technique should work just fine, but there's a minor problem. You're constantly shouting into the room, which means that it's difficult for you to hear quiet responses and it's difficult for other people to carry on conversations. What else can we do? Can we use those random sounds for anything?

Yes! A smarter approach is to wait for an anonymous sound, then start asking whether a friend you know isn't present has just arrived:

This way, you're not constantly asking the room for all of your friends. Efficient!

This technique is a very simplified description of how montior works for devices like cell phones (friends on a list) and beacons (announce a name out loud). This also gives an idea of how monitor uses anonymous sounds to reduce the number of times that it has to send inquiries into the Bluetooth environment.

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Oversimplified Technical Background

The Bluetooth Low Energy spec was designed to make connecting Bluetooth devices simpler for the user. No more pin codes, no more code verifications, no more “discovery mode” - for the most part. It was also designed to be more private than previous Bluetooth implementations. That said, it’s hard to maintain privacy when you want to be able to connect to an unknown device without intervention.

Name Requests

A part of the Blueooth spec is a special function called a name request that asks another Bluetooth device to send back a human-readable name of itself. In order to send a name request, however, we need to know a private (unchanging) address of the target device.

Issuing a name request to the same private mac address every few seconds is a reliable - albeit rudimentary - way of detecting whether that device is "present" (it responds to the name request) or "absent" (no response to the name request is received). However, issuing name requests too frequently (e.g., every few seconds) uses quite a bit of 2.4GHz spectrum, which can cause interference with Wi-Fi or other wireless communications.

Not all devices respond to name requests, however. For example, beacon devices do not respond.

Connectible Devices

Blueooth devices that can exchange information with other devices (almost always) advertise a random/anonymous address that other devices can use to negotiate a secure connection and receive the first device's real, private, Bluetooth address. Using a random address in this way when publicly advertising prevents bad actors from tracking via passive Bluetooth monitoring.

Beacon/Advertising Devices

The Bluetooth spec has been used by Apple, Google, and others to create additional standards (e.g., iBeacon, Eddystone, and so on). These devices generally don't care to connect to other devices, so use of random/anonymous addresses doesn't really matter. Instead, these devices encode additional information into each advertisement of an anonymous address. For example, iBeacon devices will broadcast a UUID that conforms to the 8-4-4-4-12 format defined by IETC RFC4122.

As noted above, most beacons do not respond to name requests, even if made to the device's private Bluetooth address. So, issuing periodic name requests to beacons is not a good way to detect whether a beacon device is present or absent. However, monitoring for beacon advertisement is a reliable way to detect whether a beacon device is present or absent.

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How monitor Works

This script combines name requests, anonymous advertisements, and beacon advertisements to logically determine (1) when to issue a name request to determine whether a device is present and (2) when to issue a name request to determine whether a device is absent. The script also listens for beacons.

Known Static Addresses

monitor uses unchanging/static mac addresses for your devices that you have added to a file called known_static_addresses. These are the addresses for which monitor will issue name requests to determine whether or not these devices are present or absent.

Once a determination of presence is made, the script posts to an mqtt topic path defined in a file called mqtt_preferences that includes a JSON-formatted message with a confidence value that corresponds to a confidence of presence. For example, a confidence of 100 means that monitor is 100% sure the device is present. Similarly, a confidence of 0 means that monitor is 0% sure the device is present (i.e., the monitor is 100% sure the device is absent).

To minimize the number of times that monitor issues name requests (thereby reducing 2.4GHz interference), the script performs either an ARRIVAL scan or a DEPART scan, instead of scanning all devices listed in the known_static_addresses each time.

More specifically:

• An ARRIVAL scan issues a name request, sequentially, for each device listed in the known_static_addresses file that is known to be absent.

• Similarly, a DEPART scan issues a name request, sequentially, for each device listed in the known_static_addresses file that is known to be present.

For example, if there are two phone addresses listed in the known_static_addresses file, and both of those devices are present, an ARRIVAL scan will never occur. Similarly, if both of these addresses are absent then a DEPART scan will never occur. If only one device is present, an ARRIVAL scan will only scan for the device that is currently away.

To reduce the number of name requests that occur, monitor listens for anonymous advertisements and triggers an ARRIVAL scan for every new anonymous address.

The script will also trigger an ARRIVE scan in response to an mqtt message posted to the topic of monitor/scan/arrive. Advertisement-triggered scanning can be disabled by using the trigger argument if -ta, which causes monitor to only trigger ARRIVAL scans in response to mqtt messages.

If monitor has not heard from a particular anonymous address in a long time, monitor triggers a DEPART scan. The script will also trigger a DEPART scan in response to an mqtt message posted to the topic of monitor/scan/depart. Expiration-triggered scanning can be disabled by using the trigger argument if -td, which causes monitor to only trigger DEPART scans in response to mqtt messages.

To reduce scanning even further, monitor can filter which types of anonymous advertisements are used for ARRIVE scans. These are called "filters" and are defined in a file called behavior_preferences. The filters are bash RegEx strings that either pass or reject anonymous advertisements that match the filter.

There are two filter types:

• Manufacturer Filter - filters based on data in an advertisement that is connected to a particular device manufacturer. This is almost always the OEM of the device that is transmitting the anonymous advertisement. By default, because of the prevalence of iPhones, Apple is the only manufacturer that triggers an ARRIVAL scan. Multiple manufacturers can be appended together by a pipe: |. An example filter for Apple and Samsung looks like: Apple|Samsung. To disable the manufacturer filter, use .*.

• Flag Filter: filters based on flags contained in an advertisement. This varies by device type. By default, because of the prevalence of iPhones, the flag of 0x1b triggers an ARRIVAL scan. Like with the manufacturer filter, multiple flags can be appended together by a pipe: |. To disable the manufacturer filter, use .*.

Beacons & iBeacons

In addition, when run with the -b beacon argument, monitor listens for beacon advertisements that report themselves as "public", meaning that their addresses will not change. The script can track these by default; these addresses do not have to be added anywhere - after all, monitor will obtain them just by listening.

Since iBeacons include a UUID and a mac address, two presence messages are reported via mqtt.

Known Beacon Addresses

In some cases, manufacturers try to get sneaky and cause their beacons to advertise as "anonymous" (or "random") devices, despite that their addresses do not change at all. By default, monitor does not report presence of anonymous advertisement devices, so to force monitor to recognize these devices, we add the "random" address to a file called known_static_beacons. After restarting, monitor will know that these addresses should be treated like a normal beacon.

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Home Assistant Example

Example with Home Assistant

Personally, I have four raspberry pi zero ws throughout the house and garage. My family spends most of our time on the first floor, so our main monitor node or sensor is on the first floor. Our other 'nodes' on the second and third floor and garage are set up for triggered use only - these will scan for ARRIVAL and DEPART only in response to mqtt messages, with option -tad. The first floor node is set up to send mqtt arrive/depart scan instructions to these nodes by including the -tr flag ("report" to other nodes when an arrival or depart scan is triggered).

The first floor constantly monitors for beacons (-b) advertisements and anonymous advertisements, which may be sent by our phones listed in the known_static_addresses file. In response to a new anonymous advertisement, monitor will initiate an ARRIVAL scan for whichever of our phones is not present. If one of those devices is seen, an mqtt message is sent to Home Assistant reporting that the scanned phone is "home" with a confidence of 100%. In addition, an mqtt message is sent to the second and third floor and garage to trigger a scan on those floors as well. As a result of this configuration, when we leave the house, we use either the front door or the garage door to trigger an mqtt trigger of monitor/scan/depart after a ten second delay to trigger a departure scan of our devices that were previously known to be present. The ten second delay gives us a chance to get out of Bluetooth range before a "departure" scan is triggered. Different houses/apartments will probably need different delays.

More specifically, each of these monitor nodes uses the same name for each device so that states can be tracked easily by Home Assistant. For example, on each node, my known_static_addresses file looks like this (note that 00:00:00:00:00:00 is an example address - this should be your phone's private, static, Bluetooth address):

00:00:00:00:00:00 alias #comment that is ignored

The address I want to track is separated by a space from the alias that I want to use to refer to this device in Home Assistant. If you prefer to use the address instead of an alias, set the value PREF_ALIAS_MODE=false in your behavior_preferences file.

In this manner, Home Assistant receives mqtt messages and stores the values as input to a number of mqtt sensors. Output from these sensors is combined to give an accurate numerical occupancy confidence:

- platform: mqtt
  state_topic: 'monitor/first floor/alias'
  value_template: '{{ value_json.confidence }}'
  unit_of_measurement: '%'
  name: 'First Floor'

- platform: mqtt
  state_topic: 'monitor/second floor/alias'
  value_template: '{{ value_json.confidence }}'
  unit_of_measurement: '%'
  name: 'Second Floor'

- platform: mqtt
  state_topic: 'monitor/third floor/alias'
  value_template: '{{ value_json.confidence }}'
  unit_of_measurement: '%'
  name: 'Third Floor'

- platform: mqtt
  state_topic: 'monitor/garage/alias'
  value_template: '{{ value_json.confidence }}'
  unit_of_measurement: '%'
  name: 'Garage'

These sensors can be combined using a min_max:

- platform: min_max
  name: "Home Occupancy Confidence"
  type: max
  round_digits: 0
  entity_ids:
    - sensor.third_floor
    - sensor.second_floor
    - sensor.first_floor
    - sensor.garage

Thereafter, I use the entity sensor.home_occupancy_confidence in automations to control the state of an input_boolean that represents a very high confidence of a user being home or not.

As an example:

- alias: Occupancy On
  hide_entity: true
  trigger:
    - platform: numeric_state
      entity_id: sensor.home_occupancy_confidence
      above: 10
  action:
    - service: input_boolean.turn_on
      data:
        entity_id: input_boolean.occupancy

- alias: Occupancy Off
  hide_entity: true
  trigger:
    - platform: numeric_state
      entity_id: sensor.home_occupancy_confidence
      below: 10
  action:
    - service: input_boolean.turn_off
      data:
        entity_id: input_boolean.occupancy

If you prefer to use the device_tracker platform in Home Assistant, a unique solution is to use the undocumented device_tracker.see service:

As an example:

- alias: Andrew Occupancy On
  hide_entity: true
  trigger:
    - platform: numeric_state
      entity_id: sensor.andrew_occupancy_confidence
      above: 10
  action:
    - service: device_tracker.see
      data:
        dev_id: andrew
        location_name: home
        source_type: bluetooth

- alias: Andrew Occupancy Off
  hide_entity: true
  trigger:
    - platform: numeric_state
      entity_id: sensor.andrew_occupancy_confidence
      below: 10
  action:
    - service: device_tracker.see
      data:
        dev_id: andrew
        location_name: not_home
        source_type: bluetooth

For more information, see here and here.

Advanced Configuration Options & Fine Tuning

Fine Tuning

1. Observe output from monitor to tune filters:

sudo bash monitor.sh 

Observe the output of the script for debug log [CMD-RAND] lines including [failed filter] or [passed filter]. These lines show what anonymous advertisement monitor sees and how monitor filters those advertisements. In particular, cycle the Bluetooth power on your phone or another device and look at the flags value, the pdu value, and the man (manufacturer) value that appears after you turn Bluetooth power back on. Remember, the address you see in the log will be an anonymous address - ignore it, we're only focused on the values referenced above.

0.1.xxx 03:25:39 pm [CMD-RAND]  [passed filter] data: 00:11:22:33:44:55 pdu: ADV_NONCONN_IND rssi: -73 dBm flags: 0x1b man: Apple, Inc. delay: 4

If you repeatedly see the same values in one or more of these fields, consider adding a PASS filter condition to the behavior_preferences file. This will cause monitor to only scan in response to an anonymous advertisement that passes the filter condition that you define. For example, if you notice that Apple always shows up as the manufacturer when you cycle the power on you phone, you can create an Apple filter:

PREF_PASS_FILTER_MANUFACTURER_ARRIVE="Apple"

If you have two phones, and one is Apple and the other is Google, create a bash or statement in the filter like this:

PREF_PASS_FILTER_MANUFACTURER_ARRIVE="Apple|Google"

If your phone shows as Unknown, then it is best to disable the filter entirely - some phones will report a blank manufacturer, others will report a null value... it's much easier to try and filter with another value:

PREF_PASS_FILTER_MANUFACTURER_ARRIVE=".*"

Similarly, we can create a negative filter. If you or your neighbors use Google Home, it is likely that you'll see at least some devices manufactured by Google. Create a fail filter condition to ignore these advertisements:

PREF_FAIL_FILTER_MANUFACTURER_ARRIVE="Google"

Filters are a great way to minimize the frequency of name requestning, which causes 2.4GHz interference and can, if your values are too aggressive, dramatically interfere with Wi-Fi and other services.

2. Standard configuration options:

When monitor is first run, default preferences are created in the behavior_preferences file. These preferences can be changed, and in many cases should be changed depending on your Bluetooth environment (how many devices you have around you at any given time). A table below describes what these default variables are:

Option	Default Value	Description
PREF_ARRIVAL_SCAN_ATTEMPTS	1	This is the number of times that monitor will send a name request before deciding that a device has not yet arrived. The higher the number, the fewer errors on arrival detection but also the longer it may take to recognize all devices are home in a multi-device installation.
PREF_DEPART_SCAN_ATTEMPTS	2	This is the number of times that monitor will send a name request before deciding that a device has not yet departed. The higher the number, the fewer errors on departure detection but also the longer it may take to recognize all devices are away in a multi-device installation.
PREF_BEACON_EXPIRATION	180	This is the number of seconds without observing an advertisement before a beacon is considered expired.
PREF_MINIMUM_TIME_BETWEEN_SCANS	15	This is the minimum number of seconds required between "arrival" scans or between "departure" scans. Increasing the value will decrease interference, but will also increase arrival and departure detection time.
PREF_PASS_FILTER_ADV_FLAGS_ARRIVE	.*	See above.
PREF_PASS_FILTER_MANUFACTURER_ARRIVE	.*	See above.
PREF_FAIL_FILTER_ADV_FLAGS_ARRIVE	NONE	See above.
PREF_FAIL_FILTER_MANUFACTURER_ARRIVE	NONE	See above.
PREF_ALIAS_MODE	true	Disable or enable alias mode; if disabled, MQTT messages are sent using a device's mac address.

3. Advanced configuration options:

In addition to the options described above, there are a number of advanced options that can be set by the user. To modify any of these options, add a line to the behavior_preferences file.

Option	Default Value	Description
PREF_INTERSCAN_DELAY	3	This is a fixed delay between name requests. Increasing the value will decrease interference, but will decrease responsiveness. Decreasing the value will risk a Bluetooth hardware fault.
PREF_RANDOM_DEVICE_EXPIRATION_INTERVAL	75	This is the interval after which an anonymous advertisement mac address is considered expired. Increasing this value will reduce arrival scan frequency, but will also increase memory footprint (minimal) and will decrease the frequency of depart scans.
PREF_RSSI_CHANGE_THRESHOLD	-20	If a beacon's rssi changes by at least this value, then the beacon will be reported again via mqtt.
PREF_RSSI_IGNORE_BELOW	-75	If an anonymous advertisement is "farther" away (lower RSSI), ignore the advertisement
PREF_HCI_DEVICE	hci0	Select which hci device should be used by monitor
PREF_COOPERATIVE_SCAN_THRESHOLD	60	Once confidence of a known device falls below this value, send an mqtt message to other monitor nodes to begin an arrival scan or a departure scan.
PREF_MQTT_REPORT_SCAN_MESSAGES	false	This value is either true or false and determines whether monitor publishes when a scan begins and when a scan ends
PREF_PERCENT_CONFIDENCE_REPORT_THRESHOLD	59	This value defines when a beacon begins reporting a decline in confidence
PREF_PASS_FILTER_PDU_TYPE	Various. See FAQ.	These are the PDU types that should be noticed by monitor
PREF_DEVICE_TRACKER_REPORT	false	If true, this value will cause monitor to report a 'home' or 'not_home' message to ... /device_tracker conforming to device_tracker mqtt protocol.
PREF_DEVICE_TRACKER_HOME_STRING	home	If PREF_DEVICE_TRACKER_REPORT is true, this is the string that is reported to the device_tracker when the device is home.
PREF_DEVICE_TRACKER_AWAY_STRING	not_home	If PREF_DEVICE_TRACKER_REPORT is true, this is the string that is reported to the device_tracker when the device is not home.
PREF_DEVICE_TRACKER_TOPIC_BRANCH	device_tracker	If PREF_DEVICE_TRACKER_REPORT is true, this is last path element of the mqtt topic path that will be used to publish the device tracker message.
PREF_ADVERTISEMENT_OBSERVED_INTERVAL_STEP	15	This is the minimum interval (in seconds) used to estimate advertisement intervals reported in the MQTT message.
PREF_DEPART_SCAN_INTERVAL	30	If using periodic scanning mode, this is the minimum interval (in seconds) at which depart scans are triggered automatically.
PREF_ARRIVE_SCAN_INTERVAL	15	If using periodic scanning mode, this is the minimum interval (in seconds) at which arrive scans are triggered automatically.

RSSI Tracking

This script can also track RSSI changes throughout the day. This can be used for very rudimentary room- or floor-level tracking. Only devices in known_static_addresses that have been paired to a monitor node can have their RSSI tracked. Here's how to pair:

1. Stop monitor service:

sudo systemctl stop monitor

2. Run monitor with -c flag, followed by the mac address of the known_device to connect:

sudo bash monitor.sh -c 00:11:22:33:44:55

After this, follow the prompts given by monitor and your device will be connected. That's it. After you restart monitor will periodically (once every ~1.5 minutes) connect to your phone and take three RSSI samples, average the samples, and report a string message to the same path as a confidence report, with the additional path component of /rssi. So, if a monitor node is named 'first floor', an rssi message is reported to:

topic: monitor/first floor/00:11:22:33:44:55/rssi
message: -99 through 0

If an rssi measurement cannot be obtained, the value of -99 is sent.

Report known states

It is also possible tell monitor to report all currently known device states by sending an MQTT message to something like monitor/first floor/KNOWN DEVICE STATES. monitor.sh will then iterate over all known static addresses and report the current confidence level. This may be useful in home assistant to get the current state after a home assistant restart.

Anything else? Post a question.