I want to put together the following; A small battery powered sensor/dongle (which I'm thinking would be some form of bluetooth device) that could be attached to a physical object - say a power-drill or rucksack etc. This sensor/dongle would be communicating with my cell/mobile phone such that if the physical object is moved beyond a preset range (say 6 feet) from the cell/mobile phone its communicating with, then the phone would detect this "out of range" event, and, via an app on the phone (which I'd write) would cause the phone to show/sound an alert of some sort on the screen and/or audibly. So, a couple of questions; 1) Is there anything that does this already? 2) Can anyone recommend a suitable sensor/dongle that could communicate with the phone - I'm thinking a basic bluetooth-connected sensor of some sort? 3) Is bluetooth the right way to do this? Many thanks! Russ.