Amazon’s branded Dash Buttons were introduced in March 2015, allowing products to be easily re-ordered with a single click of the battery-powered device — not to be confused with the unbranded UK AmazonFresh version (which works like a miniature version of the popular hands-free Amazon Echo).
As an inexpensive (US$4.99) wifi-enabled IoT device, in less than 3 months they were starting to be re-purposed. There are a handful of approaches, from fairly non-technical ARP probe detection through to bare-metal reprogramming. Amazon themselves are also reaching out to developers and smaller brands with their Dash Replenishment Service.
Getting started seems pretty simple — when you get a Dash button, Amazon gives you a list of setup instructions to get going. Just follow their list of instructions, but don’t complete the final step . Do not select a product, and just exit the app.
Most techniques use something like IFTT to connect the button event to a IoT trigger of your choosing. Instructables has a great step-by-step tutorial, and there’s some great open-source code available on GitHub.