I can second gadget_guy's post.
The WMR200 will support 10 temperatur/hygro sensors total. If you get the THGR810 sensors, they also have the display on them. The display itself shows all of them, but not at the same time. you can scan through them manually, or have unit switch sensor continously. I have 1 additional indoor for now, but planning on getting 3-4 more. The sensors are reasonably priced as well (imo).