send an email when failover occurs

Actually, most likely the simplest way is to monitor the System Id (from the System::SystemInfo::get_system_id() method). This is a UUID that is based in the primary mac on the system. If a failover occurs and you are monitoring the system on the shared address, the value of the system id will change. You could alternately use one of the serial numbers from the System::SystemInfo::get_system_information() method as this identifier. Another option is the Networking::AdminIP::get_list() that will return a list of the admin ip addresses on the device.

Logic is as follows:

String id = get_unique_id();
while (1)
{
  String id2 = get_unique_id();
  if ( id2 != id )
  {
    send_email_to_someone();
    id = id2;
  }
  // Don't flood the BIG-IP with calls.  Sleep in between requests.
  sleep_some_amount_of_time();
}

Hope this helps...

-Joe