Wired Zone Expanders
If you have a hardwired alarm system, then it is likely that you are using some hardwired alarm sensors with your setup. After all, the biggest reasons to use a hardwired system is because you want to integrate your hardwired sensors with your building. But if you plan to add a large number of hardwired sensors, then you may need to get one or more wired zone expanders to complete your setup.
Hardwired sensors connect with the zone terminals on the panel or on a wired zone expander. Since some of the wire runs may be difficult, it is usually much easier to install a wireless alarm system. But if you do decide to go the hardwired then you will need to make sure you have all the necessary equipment to complete the process. And if you have a lot of hardwired sensors that you plan to use, then wired zone expanders are a necessity.
Every hardwired panel only has a finite number of wired zone terminals. Although many hardwired panels support zone doubling, you will eventually need wired zone expanders to increase your number of zones. These zone expanders will increase the number of available zone terminals so that you can add new sensors. The zone expanders can normally be mounted in a similar metal enclosure as what is used with your hardwired panel. If you only have a small number of expanders, then they can probably be fit in the same enclosure.
Keep in mind that available hardwired zone terminals is not the equivalent to the number of available panel zones. Most hardwired panels can also support wireless sensors if you add a wireless receiver. Really, you can have a mix of hardwired and wireless sensors on your wired alarm control panel. Just keep in mind that both the wireless and wired sensors will count towards the total panel zone limit. If you reach the total zone limit, then you will not be able to add any additional zones.
Adding a hardwired zone expander increases the number of hardwired zone terminals your panel has available, not the total number of zones that your panel can support. You can keep adding new hardwired zone expanders to support additional hardwired sensors, as long as your panel still has open zone slots available. Keep in mind that the total number of panel zones is usually much greater than the number of wired zone terminals available. It's just important to keep the total number of available zones in mind if you plan on adding a very large number of zones
Also remember the the wired zone expanders you use are compatible with your system. You will generally want to purchase wired zone expanders from the same manufacturer as your system. This will ensure that they can work properly. Always check compatibility before making your purchasing decision. This can save you a lot of trouble when you go to install your zone expanders.