I can confirm that Android devices are only tracked when they actively scan for other BT devices. Tested with Samsung Galaxy S8 and A3.
Mine are hidden and have been detected
edit: if you go to the link i sent above yours, can you see your mac addresses in there, even when the phones themselves aren’t scanning?
Came here to ask exactly this.
I get the same behaviour. If my phone is not scanning, the Home does not see it.
I also have a Galaxy S8+
I guess there is no workaround for this, right?
I am at my home with no other devices around.
There is a good chance that the reason people are seeing multiple random MAC addresses is due to all the people who complained about privacy several years ago - who did not want to be tracked by MAC address. iOS devices since iOS v8 use random MAC addresses when they are scanning for networks to connect to.
the device needs to be locked to start randomzing its MAC address.
from: More details on how iOS 8's MAC address randomization feature works (and when it doesn't) - 9to5Mac
Android devices since v8 (Oreo) also give random MAC addresses out when probing for networks to connect to.
See: Implementing MAC Randomization | Android Open Source Project
EDIT2: More information about Bluetooth LE privacy - https://blog.bluetooth.com/bluetooth-technology-protecting-your-privacy in general both iOS and Android will only present the REAL MAC address of the device when they are paired to another device. But the address they advertise while scanning for a device / network to connect to - is NOT the real address.
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Without arguing about the Randomization stuff too much, the bluetooth location tracker with the RPI works just fine with Android as well as IOS bluetooth devices and we never had to pair them.
iOS appears to only randomise the MAC address on boot, Android 8 (Oreo) and 9 (Pie) are still relatively new, prior to Pie manufacturers had to enable the functionality, it appears like with Pie this happens automatically. You can see from the Android docs this started with v6 Cambios en Android 6.0 | Android Developers it clearly states
When a device running Android 6.0 (API level 23) initiates a background Wi-Fi or Bluetooth scan, the operation is visible to external devices as originating from a randomized MAC address.
This obviously does not affect every Android device out there, because Android being what it is - some devices probably have the feature disabled by manufacturers, but some devices will have this feature turned on and it would explain why people above are reporting multiple non existent MAC addresses being reported.
It is worth noting however, that LE Privacy is a core part of the Bluetooth v4 spec, and as such while it may well work great right now (for some people), going forward more and more devices will report a different random MAC address when probing for devices.
Did you find any solution? Adding multiple homes it would be great.
No, they do not appear in the scan results - only when I start scanning on the mobile device.
Both devices are running on Android Oreo btw.
Talked to google support about this. I told them I was interested in seeing all ble devices even the ones not activly scanning. Told them I want this for precense and they recommended me to send a feedback from Ghome with this request/feature for the devs to look at
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random thought… What are your phone’s location settings set to? One of the options will use bluetooth and wifi. I have mine (One plus 5, oreo) set to “high accuracy” and it shows in scan results on the home without me having to scan anything from the phone. It might not be relevant, just an idea
Got my samsung s9 with high accuracy and that doesn’t work. My Pi3 sees it when it scans so it is possible. its software related
I’ve previously used the BLEtracker to detect when we get home. I have BLE tags on our house keys to detect this. I setup the Google home detection but notice that the connection is very intermittent. Anyone else having this issue?
Have you changed the rssi? I think it’s -70 by default, set it to -90 or something
I have it set to -120. The keys are no more than 5 meters away too
great news!
finally I can scan for BT devices without any stress to my RaspberryPi! 
regarding the “combine all trackers to one” [bt/wifi/gps etc.] AFAIR there are plans to create a new “person” entity, which would combine all different device trackers used to locate people in the house
also - about the Google Home device tracker component itself - we need to have the possibility to enter couple of Google Home’s and to identify them. that would be great for room presence monitoring!
At the moment adding more than one device seems to completely cripple it. Everything slows down and there are a lot of timeout warnings. It’ll be good when it’s fixed though
Unfortunately it does not work either when I set my Galaxy S8 to “high accuracy”, just tested it… 
That is correct…
my bad… sorry about that… there is a PR active to fix issues when using multiple units
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See if you can see those BLE devices with a bluetooth LE phone app.