How to automatically send a push notification when content is created?
Use the Rules integration of the Push Notifications module. Refer to the issue "Add support for Rules module" for more details on this (issue status = needs review ...) and also use the appropriate patch from that issue.

For the "event" part of such rule to be created, just use "After saving content", limited to (= Rules condition) content type "alert".

If you have to still install the Rules module, you'll discover tons of other use cases to also be resolved by the same Rules module (possibly complemented with the Flag module soon ...).