Thanks to Bluetooth Low Energy, we are going to be seeing a lot more of these kinds of proximity beacons (Previous example: StickNFind). One interesting application of the $29 SpotLoss keychain fob is that you can create a computer log that shows when your son or daughter comes home at night.
The range of the device is 50 meters (164 feet) and works through walls and other solids
— Runs for a year on replaceable watch battery without recharging
— Uses a free app that allows users to easily customize settings
— Get texts or emails about proximity events
— Works with iPhone 4s, iPhone 5, iPad 3, iPad 4, and iPad Mini
— Will work with Android Bluetooth 4.0 devices shortly
— Uses Bluetooth Low Energy (a.k.a. BlueSmart) protocol so the battery use is minimal
— 5.6 x 3.0 x 1.5 cm carabiner style easily attaches to almost anything— Connect up to ten devices to one phone or computer at the same time
— Connects with cell phones and computers in a many-to-many relationship
— Fob supports vibrating and variable pitch alerts
— Printed circuit boards and their enclosures will be assembled in Upstate New York