So it sounds like the Iris motion sensors are the favorite. They appear to work well and the price is great. They have a 4 pack for $65 (after $10 off coupon). That seems like a really good price point. I also found this discussion and these can be calibrated to be accurate within 1 degree.
The other option that I saw is the Iris window and door sensors. Does anyone have experience with these? Lowes has a 4 pack for $53 (after $10 coupon). To bad they don’t have a pack with 2 of each.