We do not recommend the use of more than one monitor in the same home due to the possibility of Interference challenges. This interference can occur whether you choose to go with a digital or analog monitor, video or audio. The same is true when using one receiver with two transmitters or one transmitter with two receivers. Unless the system is designed to accept additional cameras/receivers, putting two systems together within the same household could potentially cause undesirable feedback and operation.
Should you choose to use 2 monitor systems in your household, it would need to be at your own discretion. You would have to unplug one system to use the secondary system in all above situations.