Dan wrote:
I know this is off topic, but I know some of you know the answer.

I need to monitor the temperature of a heating element. I need to know
when it is on and when it is off. I don't need to know the
temperature, just that when it is getting hot and when it is not hot.
(...)

http://www.amveco.com/pdf/AC1020_11-01.pdf
http://rocky.digikey.com/WebLib/Amve...15,AC-1020.jpg

This is Digikey TE-1020-ND, a current transformer. Its small and will fit within a 1" cube.
Disconnect the defrost heater and thread its wire through the hole in the middle of this
part, then reconnect it. Solder a 100 ohm 1/8W resistor across the output of the
transformer. Every amp flowing into your defrost heater will now be indicated by a
voltage of about 0.1V AC at the output of the transformer, across the resistor.

Connect one of these loggers (US$25.00)to the output of your current transformer and log
the data to your PC.

http://www.dataq.com/products/startkit/di194rs.htm

That's what I would do.

--Winston