Start an <a rel="nofollow noopener" href="/reference/event-handler">event handler</a> (part of the program that will run when something happens, like when a button is pressed). This handler works when you touch pin <code>0</code>, <code>1</code>, or <code>2</code> together with <code>GND</code>, and release it within 1 second. When you are using this function in a web browser, click the pins on the screen inst…