Each notch network has a channel that the devices use to communicate with one another. When you use several notch kits in one room, make sure that each set of notches’ channel differs from the others to avoid radio interference.
You can set the notches’ channel on the My Notches tab, tap “set channel”. Make sure only yours, and all of your devices are turned on. Otherwise, you may set the other users’ channel as well, or you will create a subset in a different channel that will not be able to communicate with the rest. To merge the channels, put each device on the same channel.