I also think that you can develop bracelets. Users connect their bracelet with their accounts. Make settings, what percentage of interest should be similar. And when in radius of 30 metres you meet someone with bracelet then your device should make a signal.
Why use a bracelet, because such a binding can be done in the application. This feature has already been used by one of the applications on the market. A bracelet is an additional cost for production.
Well, first it's additional profit from device selling, second it if you will use phone then app should show you a photo, and meaby profile to let you know who concrete is near, in bracelet case he\she will see you and vice versa and you will see her\his reaction to the signal. I don't know, maybe indeed it isn't needed, but many cultures use something like that to show that you looking forward a couple.