These have been around for many many years, packaged to just about every market.

If in a pretty plastic bear shaped colored case, they are child separation alarms. If they are in a much more professional black case, they are a laptop separation alarm. They all work the same way, when something is whatever the range of the device is, both start beeping so you know it's missing and you can follow the sound to find it.

All over the internet for $20 or so, if all you want to know if something moves too far from you. If you want GPS and the rest to track it, of course it will cost a bit more.