Meet the Pairable KEY: a discreet device that acts as a personal tracker, sensor, and remote. Just attach it to keys, purse, and other items to track them on your phone. It is also possible to set motion alerts, so you will know when someone has moved your things. KEY has a built-in temperature sensor to let you know about your environment.
The KEY can be used to control your phone and other IFTTT devices. The device is water resistant and has a replaceable battery. Sets you back under $40 at this time.[where to get it]