You can use the host availability monitor to help you determine whether a host is up or not. It will ping the host and if gets a response it will return a one otherwise, it will return a zero. There are other options such as a TCP check as well. You can then use the measure that is created for the task to create incidents and throw alerts.
You could also look into the agent availability measure. This only tells you when the agent is down which could be an issue with the JVM or the host but it is an option if you prefer to avoid plugins.