I live in an apartment with central heat. It's controlled by a round Honeywell thermostat. The heater ticks really loudly and annoyingly when it heats up and cools down (probably a topic for a separate thread), and the Honeywell thermostat causes it to heat up and cool down too frequently for my liking.
My plan is to replace the Honeywell thermostat with an Arduino board that'll have better hysteresis, plus show a more accurate temperature readout. (The Honeywell thermostat's current temperature reading is way off.)
There are two wires going to the Honeywell thermostat: a red and a beige. From my research (http://diy.stackexchange.com/questions/8019/is-there-a-standard-wiring-scheme-for-ac-heater-thermostats), that should be the standard hot and common at 24V.
However---and this is why I am writing---when I measure the voltage between those wires with a voltmeter, I end up with 0 V. The heater works fine with the Honeywell thermostat, so I cannot explain this. I have not tried closing the circuit manually, since now I don't know what to think.