Simple shell script based on bash which monitor a host with command line ping. Just bash and ping are the unique dependencies. Only state change are going to be printed:

#!/bin/bash

IP="THE_IP_TO_MONITOR"
STATE="offline"

show_state()
{
  echo "$(date '+%Y-%m-%dT%H:%M:%S') - " + $STATE;
}

while true;
do
  ping -c 4 $IP > /dev/null 2>&1
  if [ "$?" = "0" ]; then
    if [ "$STATE" = "offline" ];
    then
      STATE="online"
      show_state
    fi
  else
    if [ "$STATE" = "online" ];
    then
      STATE="offline"
      show_state
    fi
  fi
  sleep 10
done