Can I use a windows 10 computer with Bluetooth as a trusted device for Smart Lock? I have a desktop computer with an old Bluetooth 2.0 dongle and a HP laptop with Bluetooth 4.0 that I can pair successfully to my LG G3 running stock Android 5.0, but when Secure Lock asks me if I want to add that device as a Trusted Device, it fails and it tells me that I can't use that device. 

Can a Windows machine be used as a trusted device at all or do I have to change some setting?
There is some evidence suggesting it can be done, however only devices that are currently connected and in range can be enabled,  so make sure you're connected to the device you want to use i.e Windows 10


  Device-to-device e.g tablet, PC (as opposed to device-to-peripheral e.g smartwatch ) connections only remain established during the time of need such as data transfer. 


Some users have suggested using Bluetooth services on PC, to keep constant connection. Examples include Bluetooth audio service, or  connecting the PC an input device (remote control), Obex or even DUN so as to prevent connection  drop.

Credits

Trusted devices not staying connected