Connect an Announement App across the entire site and subsites

Hi,

I am trying to add an Announcement app that when filled out and started, will populate across my entire site.  For instance if our HMS system goes down (it's on a different server) I need to let all hospitals/departments in the organization know immediately.  I wanted to create an Announcement app that will "pop" up or show across the header of all pages and subsites for the organization.  Currently I have about 150 subsites, between departments and hospitals.

I am using Sharepoint Foundation OOTB, no Designer or Visual Studio.  Is this possible?

Thanks in advance for all your help.

Diane