HipKey

Keep track of your phone, your belongings, or even your kids with the HipKey ($90). This aluminum and plastic disc pairs with your iPhone or iPad via Bluetooth Smart, alerting you at your chosen distance when the two drift too far apart. Keep it in your pocket to make sure you don't forget your phone, keep it in a bag to make sure no one tries to take it, or clip it to your kid's belt loop to ensure they don't wander off. There's even a motion mode that will trigger the alarm if anyone so much as moves the key — but in any case, it'll typically give you one less thing to worry about.