Environmental Monitoring

[Ben Scott]

  It's probably worth mentioning that most motherboards built within
the past 5 years or so have some capabilities for monitoring.  Most
have at least one temperature sensor.  If all you're interested in is
making sure your equipment isn't overheating, this will often do the
job.

  Along with temperature, many boards have one or more fan-speed
monitors.  Many also have connections for one or more switches for
things like chassis intrusion detection, front panel "sleep" buttons,
and so on.  All of these can be re-tasked for other things.  You could
connect the "sleep" pins on the motherboard to whatever random
contact-closure sensor you have, and then trap the event using ACPI. 
Crude, but workable.