For the input you could use the list setting type: https://github.com/jokob-sk/Pi.Alert/blob/941a8ef66171d32ccfedbc9d79be03a08f18aa7a/front/plugins/website_monitor/config.json#L352

or create a different input form control for a new setting type.

The list setting type is then resolved like this:

The actual implementation can be found here: https://github.com/jokob-sk/Pi.Alert/blob/941a8ef66171d32ccfedbc9d79be03a08f18aa7a/front/settings.php#L248

I just tried the current scan table but it needs a scan id and I did not see an easy way of generating the right one.

I think it's not really used and it's fine to use the number 1

I've added some quick docs on teh DB structure: https://github.com/jokob-sk/Pi.Alert/blob/main/docs/DATABASE.md

yes, I tried that as well and I can add the data.
I discovered that the plugin mapping to tables happens after the scan is finished. So adding more records to the CurrentScan table does not help, as at the start of the next scan it gets deleted (see def save_scanned_devices (line 1248 in pialert.py) ) .
So the plugin data never goes anywhere.
We would need t do the data mapping after the scan but before the processing of the scan.

With DHCP_Leases it works.

I have a working version now I believe.
Is there a special way you would like me to test it or to submit a PR?
https://github.com/Data-Monkey/Pi.Alert/tree/undiscoverables_plugin