Been there, done that. First of all, if your computer isn't connected 24/7, what's the point of sending email? You first have to determine why you are monitoring, and what you want to do if something fails, before deciding what you are going to use to monitor. Are you monitoring a mission critical application? Do you (or someone else) have to perform a manual intervention if a service is unreachable? Are you just monitoring to get an indication of your weekly uptimes?

I've monitored services in several previous gigs. That included using off-the-self products like mon, big brother, and mrtg, and products written from scratch, which either ran 24/7 or ran from cron. Sometimes the monitor ran on the same box that performed the service - and sometimes the monitor was a spin in a web, monitoring services of a range of machines. Sometimes, all they did was producing graphs, some products send out messages to pagers and phones, some tools tried to fix problems instead of reporting them, and sometimes they did all three. And I've written monitors to monitor my monitors.

I've written scripts as simple as:

#!/bin/sh
if ping -c 1 'xxx.xxx.xxx.xxx'
then :
else /etc/init.d/network restart
     echo "Restarted the network"
fi
[download]

and programs with thousands of lines monitoring dozens of functions of tens of database servers, with cascading alerts.

Abigail