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Problem I'm trying to solve: I want some sort of bluetooth token that would always be in my pocket/backpack (e.g. on my keychain), and I want to lock my phone automatically when it loses connection with the token (i.e. I'm too far away from my token or if my phone is stolen).

I tested the approach by writing a script in tasker Android app, and using my bluetooth headphones as such token. It works great, however using the headphones is of course inconvenient since they aren't always connected to my phone and I'm not always using them.

I tried a couple random bluetooth tags off Ebay, and they don't really work well, they require custom apps to connect, and even though they are discoverable in my phone bluetooth settings, they don't connect to it via standard means.

I want the simplest thing -- basically my only requirement is that I can connect to the token with standard bluetooth functionality and it stays connected unless I turn the token off. Does such a device exist?

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  • Well. I post it as a comment because it is not an answer but just an attempt to explain how Bluetooth works and may be you change your reqirements. So the short answer is: Yes and No. Why yes: becasue you can use any classic Bluetooth device that supports RFCOMM, HandsFree, HeadSet or HID protocol (your Bluetooth enabled headphones, handsfree, keyboard, mouse, etc). However, s you described above, that is not good idea to use headphones us such device. And Bluetooth Classic "eats" power of your phoen and of your device. (continue in next comment) Commented Feb 26, 2023 at 21:54
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    The next class is BLE devices. There are also HID and Audio devices but when connected we back to the same problem as with classic devices, except it is more power safe. And of course, to be able to lock your phone you any way need third-party application. Of course you always can "order" custom device (tag) development for both: Bluetooth Classic and Bluetooth LE. But we back to power problem. (next comment) Commented Feb 26, 2023 at 21:55
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    The solution I see is to use something like iBeacon (there are lot of cheap). It is Bluetooth LE device and does not require connection. It advertises some predefined information and your phone can receive this advertisements in background to check if device is there. Advertising also includes RSSI information that allows to caluculate more or less precision distance to the tag. Of course in this case you also need additional software that will receive the advertisements from your device and lock phone when it far away. So from my point of view this is the best solution. And BLE save a power. Commented Feb 26, 2023 at 21:58
  • @MikePetrichenko Ah thanks! So I understand I can't achieve it with BLE precisely because BLE doesn't keep constant connection? I guess if I can tolerate some power loss (I am happy to use the token only in high risk situations), then I should be looking for a regular bluetooth device? I imagine it would use even less power than actively used headphones, which isn't that bad. I guess it would also be a power drain on the token too, but similarly, headphones survive hours of active use, so if I just need to charge it now and then I'm happy with it. What would be the simplest device like that?
    – karlicoss
    Commented Feb 26, 2023 at 22:44
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    You can use BLE with permanent connection but will need to use custom application for that. And in fact I am not sure how long BLE can keep connection active (never tried such scenarious). So yes, its better to use classic for your case. Simplest device: this is good question. I am trying to remember anything that can be small and will not handle Audio. Something with just rfcomm and can;t remember nothing except hc-05. Try to look through internet something that simple support Serial Port Profile. Anythin, as you just need connection keeping. Commented Feb 27, 2023 at 7:04

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This works really well with an Android phone and Android watch. The setting is under Smart Lock - called Trusted Devices and you can in fact chose a wide array of devices

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  • Thanks, but sadly it kind of does the opposite of what I want -- it doesn't look the phone near the watch at all (unless I do extra effort with doing with via the power menu). And it keeps the device unlocked for a while even after it loses the connection with the watch (I'm not sure if it's intended or just a bug)
    – karlicoss
    Commented Sep 20, 2023 at 1:35

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