Most Z-Wave devices that are plugged in to power act as a repeater. Devices that work on battery only (such as locks and TSTATS not learned in on C-Wire) do not repeat signals.
There are devices that act as a repeater only as well. While not an exhaustive list of devices that work with the IQ PAnel 4, the below guide contains devices that have been tested compatible with the panel by Qolsys
Something like the Aeotec Z-Wave Range Extender DSD37-ZWUS could be used, but so could other light switches and plug in modules.
More information on setting up a Z-Wave network can be found below: