These systems have a wire going to every window, door, motion, fire and other sensors. For this reason they are very difficult to install in existing structures.
While hardwired system cost is lower, the installation cost will far outweigh a wireless system if you are installing it in an existing home. But they are considered slightly more secure and have lower maintenance costs.
In addition to difficulty of installation, hardwired systems usually have only six to eight zones. The zones are what the system monitors, so if you have more than six or eight sensors in your home sensors will have to be grouped together on one zone.
When sensors are grouped together it makes it more difficult to troubleshoot a bad sensor. Also, this will make it more difficult to determine where an intrusion has taken place if you are at home during a break-in.
Wireless systems have a wireless sensor at each opening. Fire, motion, glass break and other sensors are wireless as well. Wireless systems are easier to install and they can be removed from the home when you move. However, since each sensor has a battery you will have to replace them every few years.
Wireless security systems can be purchased with many zones. A 24-zone system will monitor 24 sensors; since wireless sensors are not grouped, you will know exactly which sensor has been tripped. There are systems that will audibly tell you which sensor was tripped, these are called talking units. Also, you can purchase a key fob that will allow you to arm and disarm your system at a distance; many key fobs have a panic button that will notify your monitoring facility to call the police or ambulance.