This Forum discussion will help you start doing something like you want with a Map Polygon using the MIT map component Gustavo. The example uses a FeatureCollection
https://groups.google.com/forum/#!msg/mitappinventortest/BOIzt9ag5m4/zDJdt2ImAgAJ
You can do something similar with code like this if you built your Polygon using set Polygon.Points to a List of coordinates.
When distnceToPolygon = 0, you are within the zone of the Polygon. If that happens, send your message however you want to.
What have you tried?
Regards,
Steve