Ping_Alert
Keep PING to monitor hosts and alert you when get consecutive PING loss/timeout and back to normal 

Port_Alert
Monitor TCP for server / database and alert you when get consecutive TCP ports connection timeout and restored. TCP applications such as port 21 for FTP server, 80 (http server) , 1433 (MSSQL server) ,1521 (ORACLE server),3306(MYSQL server),25(SMTP server)

CPU_Alert
Alert you when CPU or Memory keep HIGH/Low than thresholds on a continue time period . Alert you once again when back to normal