Usually the dealer/MFR will add a sticker either under the hood or under the dash if you have a OEM alarm.
They will usually include "operating instructions" in the owners manual as well.
A decent (honest) alarm shop should be able to list what you need in a few minutes. They can look the car over to see what is/isn't needed.
Also, regardless of factory alarm or keyless entry, what you will/won't need is sorta determined by the make/model of alarm/remote start being used.