Got one as well.
Works ok with my 8.0 L1520.
Obviously bluetooth must be switched on but the sensors do not show up in the paired devices list funny enough.
They work in some kind of bluetooth backround environment.
Basicly you have three options.
1. Activate an alert on the phone and sensor when the sensor becomes out of reach from the phone. The sensor makes some kind of siren noise. Phones also makes sound and vibrates (optional)
2. In the rare event you don't know where your phone is but do have the tag/sensort at hand you can page your phone.
3. This option will be used my most people I guess BUT.........doesn't function very well !!
You can page the sensor/tag with your phone in case you lost one of your belongings (keys!) say at home of office. Problem is the sound the sensor makes is just too weak !!! why Nokia ? Why ??!!
The Tag is capable of making a descent sound in the "out of range" warning mode, but with the "page from phone" function it is a different sound and simply too weak !! If for example your keys are in some kind of jacket, purse or closet, you will almost hear not the sound unless it is completely silent (and you have good ears......)
Every Lumia user should at least have one of these due to the pretty high gadget factor and it's also kind of useful.