Product review (2 stars): Failed to communicate 6 weeks after purchase.
It may be the #1 best-seller in humidity gauges, but read the negative reviews. Especially the recent ones. That will tell you that the company hasn't fixed the quality of the product for years. Apparently, the company, AcuRite doesn't read the reviews, and hasn't tried to improve the product. With some other product reviews, sometimes you will see more recent reviews with more higher start ratings. That's a hint that the quality may be improving - the company responded and fixed the quality. Not AcuRite.

This one failed in about 6 weeks - too late for an Amazon return.

With fresh batteries in both units, the outside unit transmitter light blinks red as if it is transmitting. The indoor unit has the bars progressing up, cycling over, like it is trying to receive. But no readings come from the outside unit. Even if it sitting next to the inside unit. The outside unit has been sitting under a porch awing, away from rain, sunlight. And the distance to the indoor unit was only about 15 feet. So I don't think I'm doing anything wrong here. It worked fine under those conditions up until it suddenly failed.

If I ever get it working, I will post again.

Update: Sept 25, 2015
It spontaneously started working again. I wrote the bad review Sept. 14, 2015 and about 5 days ago, it started working again. It sat for about 6 days in a box on the floor, with the readout stuck on the same number fresh batteries in. It's back in operation again, with the outdoor unit on the porch where it was before. I'll add one star. But now every time I look at it, I wonder....