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.
