Zabbix Log file monitoring for specific word
First make a script that will watch the logfile ( while :; sleep 30; ... ) and can call a function when alive is missing. Use zabbix_sender for alerting Zabbix.
Alternatively you can send a message every 30 seconds to Zabbix and make a trigger in Zabbix when it is silent, but that will cause a lot of communication (do not save historical data here).