Finally got parts for my rectifier to allow me to sense the 24 VAC thermostat lines. Works great, in the picture below you can see it is turning on the LED in response to the heat turning on.

Nothing frying yet so I guess it's all good! the rectified signal is like 32 VDC, this presumably is because the 24 VAC is an RMS value, 32ish must be the peak to peak voltage.

Next step is to hook my keyfob up and zip tie this somewhere inside my furnace control enclosure.