If you know what protocols and device identifiers your old wireless alarm system uses may be, but I think you will have to know a lot about the alarm system and how it works to stand a chance of talking to all the remote devices.
Probably not a beginners project.
Please only ask questions in the forum I will not answer questions sent to me directly via PM
Remember we want information.......................no information no help
The use of crystal balls & mind reading is not supported