I just backed a Bluetooth Tracking Device that allows you to find your keys, phone or anything else of value whilst being able to go both ways.
From the phone app to product and vice versa.
Think it is really cool and innovative. I know that their are projects out there that do similar things like Tile and TrackR but love that this product is by a startup in Scotland, don't see many coming from here. http://VkfmIDkF.kckb.st