Tag your stuff, from cats to keys to kids, with Bluetooth-based location sensor
StickNFind sensors are the size of a thick US quarter and cost $50 for a pack of two. Put them on whatever it is you want to keep track of and monitor/find them with your smart phone’s Radar Screen App; You can set an alarm to trigger when a distance boundary is exceeded. Because the app works on signal strength, it can’t immediately tell you the direction of your tagged belonging, but walking about will tell you the direction that increases the signal strength. The range is 100 feet. via SmartPlanet.