I just got given one of these wrist watches which seem to be sold singly

I was wondering if anyone knew what they were for? Do they actually
communicate with anything or does one have to have two to use it at all?
There is a scan button on it. All the ones on e-bay SEEM to be being sold by
dealers at somewhat more than their wholesale price. (and are usually being
sold singly, implying that there is some use for them as such?)

Has anyone one of these fo rswap if they can only be used in pairs?