This is a simple poker timer with an audio tag Ding! when the level changes.
Games are stored in HTML5 localStorage, with the option to share the game to the server. When a game is shared it is shown on the front screen and anyone can use the timer and add a break to the game. Breaks are synchronized across clients.
The timer requires a modern web browser, you can just open the HTML file in a web browser to use the timer. Saving the games to localStorage requires a simple web server, synchronization requires a server running PHP.