If you wants something really simple and low cost to setup, you could simply use Pushover Notifications on your phone. See the following thread for details of using Pushover "Emergency" notifications, which can make you phone produce an audible alert, even if you have it in silent/do not disturb mode while sleeping. These alerts will also repeat until acknowledged. There are some settings on your phone that also need to be tweaked to allow the Pushover mobile phone app to 'break through' your phone's silent mode.
Specifically, see this section
[E] prefix is now used for emergency notifications and requires the following parameters
retry - how often to resend notification until it is acknowledged (in seconds with a minimum of 30 seconds)
expire - timeout for resending notifications if they are never acknowledged (in seconds with a maximum of 10800)
Here is an article regarding setting up Critical Alerts on iOS. I am sure there is a similar article for Android.
https://blog.pushover.net/posts/2020/2/ios-critical-alerts
