If you're a bit technical, wiring up a hygrometer and thermometer to an Ardunio or RaspberryPI and having it send you an email, SMS or whatever is relatively easy and on my to-do list in case of thermostat failures, power outages (put your modem/wifi router on a UPS and your Thermostat) or anything else.

Once I do it, I will post up the sketch or steps to make one. I've messed with one since I made my garage door opener wifi enabled, but totally doable.