We were having humidity problems in our basement. We have a large home with 3 stories, 5 bed 3 bath, 3077 sq ft.One set of these monitors wasn't enough, so after finding that the 1st set measured temp and humidity well enough I ordered a second set. Several questions were posted here asking if more than one set of units would interfere with the other, and the only response was from customers who were guessing with no response from the seller.When I tried to sync up the second set that had the remote transmitters in different locations than the 1st set the new monitor would only show readings from the previously installed transmitters. This was true even when separating the monitors and their transmitters on different floors. The range of these units makes initial sync of more than one system impossible when they are within several hundred feet of each other in my opinion.I contacted Amazon, who was guessing also, and the seller at the email address of amirus@foxmail.com and they told me both systems would work, but their suggestion on how to make that happen didn't work. I tried several combinations of taking out the batteries of the previous units, syncing the new ones after batteries were installed, and reinstalling the batteries in the older units. I then reversed this process and neither worked, with both monitors showing the exact same reading of the transmitters that were powered up first.I then left the older units powered up, removed the batteries in the new units, got in my car and drove them to a location about a mile away. I verified that the monitor would not sync up with anything where I had driven, then removed all batteries and reinstalled the batteries in the transmitters and then the monitor, allowing them to sync up. I then placed them in a ziplock bag, drove back home and redeployed the transmitters in different locations than the older transmitters. I placed the newer monitor in the same location as the original one.So far both systems are working independently after an hour, as shown in the attached picture. I suppose, if they remain independent, that once one of the systems runs out of battery, that I will have to take that monitor and its 3 transmitters to a location out of range of any similar frequency to resync them to each other. But at least it seems to have worked. I will update this review if that changes.For reference, the picture shows the upper monitor for the upstairs (#1 1st floor outside covered deck out of the rain, #2 third story bedroom, #3 upstairs garage -not air conditioned) air conditioning on upstairs. The lower monitor for the finished basement with the separate air and heating system off (#1 family room - larger dehumidifier on, #2 basement bedroom smaller dehumidifier on, #3 downstairs garage - air conditioned but not on). The upper number on both monitors colocated in the 1st floor kitchen is the temp and humidity at the monitors, which agree within tolerances.This configuration gives us a total of 7 locations in different areas, with the colocated monitors as one, with 6 remote transmitters that work independently.I suggested to the seller that they offer a system with selectable frequencies so that separate systems could be switched to separate frequencies. Such systems do exist but the are much more expensive.Update: The separation of the transmitters lasted 3 weeks, with #2 and #3 transmitters now merging to only one of the locations. I will repeat the process of resyncing them today when I do an errand away from the house, but because they didn't maintain their separation I would not recommend buying two of these systems because they will obviously not remain independent of each other. For this reason I took away one star.The 2nd picture shows the #2 and #3 transmitter reading as merged, whereas they are in different locations that are dissimilar in temperature and humidity.