just bought 2004 blazer,it came with two keys and no fob,how can i tell if it is equipt with keyless entry or not ?

 

Covered in other threads.

The RPO code for keyless entry is AU0. If you have it, you have keyless entry.

You could also drop the driver side hush panel (plastic panel under the dash). The RKE module would be attached to this panel directly behind the DLC (data link connector).

 

does not have rpo code for keyless entry,how difficult is it to install an aftermarket system?

 

Depends. Something this new, you will likely have to have the BCM programmed for it. But you at least need to check to see if you have the wiring connector near the location of the receiver. If you do not have that, it is not worth it to try to get the factory RKE and you should just go aftermarket. If you have the connector, you could try just getting an RKE module from a junkyard and plugging it in, then getting the remotes and see if it will work.