Smart doorbells can snap a photo of whoever rings the bell, making it so you can screen all those visitors you get throughout the day. Over on Instructables, Naran shows you how to build one with a Raspberry Pi.
There are few things dorkier than using the bell on your bicycle. Once you do that, it can only lead downhill into a world of helmet mirrors, handlebar tassels and high visibility ankle bands. But you should do it anyway. Using the bike bell makes life easier for you and everyone around you.