My wife and I are expecting another child in a couple of months. We have one monitor now for our daughter. When the new baby is born, we would like to have monitor transmitters for both children. How have other people handled this situation? Did you get two sets of monitors and have two receivers everywhere? Did you get a monitor system with multiple transmitters?
The simplistic answer is to buy two from different manufacturers. But most baby monitors use the same spectrum, so there will likely be interference regardless of which models you use. Some come with a switch for a channel (or come pre-tuned to a given channel), so see if you can opt for those.
Or, you know, don't bother with a monitor for the older daughter unless she has some sort of condition that requires constant vigilance. You'll sleep better if you aren't laying there, listening as hard as you can for a noise that isn't there. (Trust me, I know! :7)
Like Torben Gundtofte-Bruun said, the newer digital devices don't have that old-school problem. Additionally, devices like the Samsung monitor we use now allow multiple cameras to be paired with each monitor. This allows you to use either monitor to view either camera.
We're expecting our next youngest in about 2 months, and I was hoping to get another one of these monitors so that they could work together. Amazon says "currently unavailable", so it's probably been replaced with a newer model. Hopefully the newer model works with the older camera.
If your kids are in the same room, I think a standard baby monitor (ie, a receiver and screen) will do for you. Plus, buying only one monitor will save you money.
If the kids are in different rooms, then you should consider getting a baby monitor that comes with multiple cameras. Such baby monitors might also come with a split-screen function to enable you to simultaneously monitor your young ones from the same screen.
That said, I highly suggest that you look for a baby monitor that doesn't use wifi. Why? Because such monitors transmit digitally and are better when it comes to multiple camera connections as they don't have issues with signal interference as experienced in the wifi models.
What's more, these non-wifi monitors are more secure--in the sense that they utilize FHSS technology which involves randomly changing the frequency of your baby's audio and video signals. This gives hackers a hard time cracking the transmission frequency at any given time.