Product review (1 stars): Don't Buy - Save Your Money
Don't waste your money.  These don't work PERIOD.

It looks nice, but, they don't work.  When it does work, the remote units can transmit the temperature from as far away as a few feet.  Just think.  You can see what temperature it is in your living room and what temperature it is 6-12 inches away.  You go much further than that, and  the display freezes with the last reading.  It will not transmit from a different room at all.  You must place them pretty much next to each other.

What's great too is when they are all together, which they must be to work, they can show three different temperatures.  I can put the main unit and two indoor remote units right next to each other and they will show 3 different temperatures, several degrees apart.

Then they just stop and go blank too.  When this happens, or the temperatures make no sense, the only way to get them to work again is to reinsert the batteries.  Of course this resets the settings so you have to redo them all each time you do this.

So, not only do these not work, they are very poorly designed for the few times they do.  They can't transmit anything more than a few feet as long as they are in the same room so there is really no point.  Then, when they do work, you have to guess what temperature.  Maybe just add the three temperatures and use the average..

Save your money.  This is a waste of money.  Look at the ad.  Each unit has a different letter name, A - B - C.  The ad has two A's and no B's, but yet shows a temperature for all four units.  How?  Two units are both set to A.  Your instructions say you can't do this.  How did you do it?  How did you set two units to the same letter, but have four temperatures appear?  Even your ad shows how ridiculous these are.  Save your money.