+Observer is a utility that is available with the dataguard. Its basic purpose is to keep the database available to the clients all the time. It is started on a separate location other than Primary and Standby locations. After starting the observer, it starts watching continuously both the sites. Whenever the PRIMARY database fails due to any reason and the connection between the PRIMARY site and the observer breaks, the observer waits for a certain time which is set up during setting the broker configuration. When this time passes, the observer automatically starts the failover process. As a result, the Physical Standby database is converted to PRIMARY database. After this failover, the users again connect to the database. This connection redirects them automatically to the new PRIMARY database.+
As far as i know, there can be only one observer for a single data guard broker configuration with the fast start failover option. Protection of the observer client or the box can be achieved on system level.