Product review (3 stars): It would be nice if the instructions mentioned that you need a sensor ...
First I ordered directly from AcuRite. They never shipped and never informed me. When I called, it took 20 minutes to find out that my order was declined. No explanation what that meant.  So I ordered from Amazon using the same card and no problem, shipped immediately.  During the install, though, the blue light suddenly disappeared and wouldn't come back on. I  assumed the unit shorted out or was defective.  I was ready to send it all back, but decided to leave it plugged in for a while in case it was a software updating issue.  Then I put batteries in one of the sensors and the base suddenly popped up on the web interface.  Still no blue light flashing or otherwise, but the unit was recognized. It would be nice if the instructions mentioned that you need a sensor sending data in order for the base to be recognized.  The temperatures shown were initially much higher than reality, and were slow to adjust, but after about 30 minutes they normalized.  It's not a perfect system, but it works.

Update: after ten days, I have to qualify that and say "it works sometimes."  The sensors are prone to failure to send a signal to the base. This can be due to location, but also due to I don't know what. I have one sensor that is no more than 2 feet from the base and has fresh batteries. The sensor status shows Signal Strength: Excellent, Battery Level: Normal, yet it has been two days since it last sent a signal to the base.