If you're a chronic misplacer of small items — or, Fek'lhr forbid, larger ones, too — then you've got some options, including keyrings that light up or make noise. Want a more robust option? The Cobra Tag uses Bluetooth, GPS and an app to form a little smartphone-and-key support network.
The Cobra Tag system will keep you from losing your phone and keys (or anything you could attach the GPS-enabled fob to) in a few different ways. You can set up an alert, for instance, whereby the phone or fob will make some noise if either one ever strays too far — Cobra defines "too far" as 30 feet. That's useful if, say, you keys fell out of your pocket while you're walking along. Failing that, you can also check in with the fob's GPS coordinates to hone in on where it is, and continue to trigger the noise until you find 'em.
It's a two-way street, too, as the fob will also let you find your phone, if that's what you're missing, and will even give it a ring so you don't have to ask a friend to.
The Tag will set you back $60. Pricey? Yes, but it sounds like you'll never lose your keys or phone or what-have-you ever again. Or, at least, you won't have a good excuse as to why you did.