How can I set alerts for warranty renewals whenever an item requires one?

You can setup a custom field of type ‘Date field (Alert)’ from More -> Custom fields -> Items.

Associate it with a specific group or all the future groups. Once created, you can then add the value for this custom field (date alert) from within the asset details page. You can set different date alerts for other assets.

So whenever a warranty is about to expire, you will get an email alert.

Also, if you set the custom field up as a recurring date alert, you’ll be able to manage repeated warranty renewals.

Note: You will only receive alert emails on the time set from Settings -> Company Settings -> Time for Alerts.