Hardwired detectors’ usage is with cons of complicated installation and distance limitation. So, Wireless alarm system is more and more popular nowadays.

Wireless detectors is more convenient for updates of existing burglar alarm and fire alarm systems. It enables it easy for the existing alarm system to add any quantity detector and change detection area, repair detection line error etc.
Of course we need a converter which will convert the wireless alarm signal to wired output and link to existing alarm panel.

For example, wireless smoke detector, wireless smoke and heat detector, wireless gas sensor can be easy to add to existing fire alarm system.
The wireless fire detectors can be added to existing burglar and Fire home security alarm panel which has the wired zones port with N/C or N/O circuit. The wireless fire detectors can be added to conventional fire alarm panel as well.

Add wireless detectors such as pir or named motion sensor, outdoor active infrared detector, door contact, smoke detector, heat detector, CO detector, Gas sensor etc. at any place you want.  Then install the wireless to wired converter at place where within the distance required.  For example, the wireless detector transmitting distance is 200m, and converter receiving distance is 150m, then the distance between converter and detector should be within 150m.  
And please make sure wireless detectors can work with the converter with same wireless coding way.  Generally, manufacturers have their own wireless coding technology for their own wireless products. So, it is important to make sure of it.