This one should work in the background: https://banglejs.com/apps/#hralarm
Thanks for the hint. It looks like this app can do the trick.
@Fteacher started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
This one should work in the background: https://banglejs.com/apps/#hralarm