Sometimes your phone rings but you don't know about it, because it's hidden on your desk or in your bag. Especially when it's on silent. There's a project pitching for funds on indiegogo, a Kickstarter-like service, at solving this problem: DrBlinky.
DrBlinky pairs up with your phone wirelessly by Bluetooth 4.0. When a call or a message or some other event comes in, DrBlinky flashes. The idea is that you clip it to your bag or something else you're more likely to see. You set up which events you want to make it flash via an app on your phone. Currently it's an Android app only, but an iPhone app is in the works.
Of course, this project is still looking for funding, so there's no guarantee it will make it to market.