The idea of customizable add-on buttons for smartphones isn't exactly new. First we had Pressy (which was quickly cloned by Xiaomi and others), then the Dimple NFC button pad came along. So what's next? Well, a Hong Kong startup thinks Dimple has space for improvement, which leads us to the Air Button. As the name suggests, this is yet another battery-less button that also makes use of -- and without interfering with -- NFC on the back of many Android devices, except it doesn't have a memory limitation as the commands are stored in the app, so you can assign literally as many actions and apps as you want. For instance, you can set it to be an emergency button that toggles an audio alert, a flashlight and a phone call at the same time. Or you can have a sports mode button that starts playing music as well as launching your preferred fitness app.