I used blueproximity successfully with my Linux laptop. I bought the smallest bluetooth headset I could find ($25), removed all extraneous parts, and carried it on my person (not my bag). It was so small that I didn't notice it. Effectively like two-factor authentication for unlocking my laptop.
It's unwise to use your phone for this purpose, because a phone and laptop might both be swiped if you're not holding on to both. This has happened to folks at cafes or on mass transit in the Bay Area.
I've tried to use blueproximity at some point (mostly for convenience because I sometimes forget to lock my screen), but the range of BT devices is too large for comfort. I could be anywhere in my flat or in the medium-sized open plan office at work and the phone in my pocket would still be in range.
Have you tried configuring it? It has a slider that you can adjust to set a minimum power level, so that if the device is too far away it locks anyway, even if it can still detect it.
It's unwise to use your phone for this purpose, because a phone and laptop might both be swiped if you're not holding on to both. This has happened to folks at cafes or on mass transit in the Bay Area.