Difference between NX-454 and NX-454 Wireless sensor?

Does anyone know what the difference is? I have a Caddx panel and have some NX-455's installed.  I want to add a few more and I found used NX-454's which look similar but I can't find any documentation.  Cost is a fraction of the new NX-455 and these are not for doors that I worry about a lot - more interested in knowing if they are open or not.  Thanks.