Taking pictures, sharing your location, and making calls are easy enough to do with an Android device, but for the most part, they all require your screen to be on with some sort of swiping and pressing actions. Dedicated shortcut keys are virtually non-existent on any modern day phone, but their utility is something that can be very useful.
Pressy is an external shortcut key that plugs into your headphone jack and works through a dedicated app. You can use it for any function you choose, such as taking pictures, turning the flashlight on and off, calling contacts, sending your location, and a lot more. Shortcuts are assigned to the number and type of "press" you make. Pressy comes in blue, red, white, and black, and is available for preorder starting at $27.
With innovation (Pressy) comes knock-offs—meet HelloKlick, the less expensive version of Pressy. This shortcut key button runs through its own Android app and is usually available for $4 or $5, although you'd be hard-pressed to find one at the moment.
The Xiaomi MiKey is another alternative to the Pressy, available for 4.9 Yuan (roughly 80 cents). It's an amazing deal to be sure, however, they are currently only available for purchase in China, like the rest of Xiaomi's products. This alternative functions in similar fashion, using its own app to program what actions presses will trigger.
If you use headphones a lot, or simply want more dedicated button functionality, the guys are Dimple.io have your solution.
These buttons simply stick onto your NFC-capable Android device and work through the Dimple app. They have a framework for plug-in development so the possibilities for use are endless. You can pre-order your Dimple for $18 for the mini (2 buttons) or $28 for the standard (4 buttons) on their site, and even combine multiple Dimples for ridiculous functionality.