This company has made a small (quarter-sized) disk with a strong adhesive backing that can be effectively tracked by a Bluetooth-enabled smartphone. It works.
The sensor comes in a variety of colors, has a light and buzzer (so it can be located in the dark), and is powered by a user-replaceable battery that lasts about a year. Although it doesn’t give direction, it provides the range, which is usually enough to “home in” on it when it appears on the tracking application (it has a range of about 100 feet). You start walking in one direction and note if you are getting closer or farther away from the disk.
There is a feature called Virtual Leash that allows you to create a virtual leash with a sticker. If that sticker moves away more than the approximate selected distance from your phone, your phone will alert you. You can even select different types of alarms for different stickers. The app can monitor several disks (they come in packs of 2 for $49.99 with several different colors available). A disk can be placed on a pet’s collar to keep track of your pal so you know if he is wandering off.
Put them on key chains that you can’t seem to keep track of, portable phones, or even luggage. You could stick a Stick-N-Find sticker on your suitcase and when all the baggage starts coming out on the belt, you can sit down and wait. Once your suitcase is within range, your phone will alert you and you can get up and take your suitcase.
You can see it in action on the company’s website: www.sticknfind.com.