I don't do hardware (although this project looks simple), but it would be interesting to own one of these and a lot of people like me might be willing to part with a few bucks for the privilege of owning one (especially if it helps spot leaks that are adding to the heating bill).
I use this one for checking the oil on my pan to see if it's hot enough for my ribeye steak:
If they used an rgb led instead of the read-out, you might be able to buy one for $5.
Many people are having insulation installed (in the UK, at least) and having a simple method to show the effectiveness would be good.
It could even be put in the sales pitch. "Here's the heat pouring out of your home. See your neighbours? That money is staying in their home."