Michael there are a couple of ways to do this depending on what you want. First you could get a Smarthub, it is able to monitor up to 10 compatible sensors and posts the Info online. Acurites 5 in 1 displays for the most part only show the data from the 5 in 1sensor, but the 01536 will show the 5 in 1 and up to 3 more compatible temp humid sensors. This 01536 display is a PC connect unit that will post data online when it is connected to a PC 24/7 but I'm not sure if it shows the extra sensors online also.
Hello Michael, Ledrak's suggestions are valid. We do have two different 5in1 display models that will allow you to add sensors. One is the 01536/06056M described above, the other is 06046M. For your convenience, I have provided links below to these displays. The smartHUB is also a good suggestion if you are interested in monitoring online. Please let us know if you have any other questions. Thank you.