A HeartBeat in the computer world is a regular (every second,minute,hour) signal or pinging of a system or service to ensure it is still running.

For example you could set up a CronJob of
{{{
wget http:<yourhomepage>
}}}
to run every 10 minutes and then send you an SMS you if your ISP was down !

See http://dictionary.reference.com/browse/heartbeat
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