Electronic Alarms and Home Security Devices - should I replace old smoke detectors?

I just bought a home that is about 9 years old. It's got hardwired smoke detectors that I have not found a lot of info on the web about (They are Firex and the only identifying number on them is 120-538b).

I'm pretty good with electric and just replacing them seems pretty easy. They have a load, a neutral and what I beleive to be is the common wore they all trip with.

My questions is this: 1) They're kinda old. Should I replace them? and 2) if I go with a newer model, say a Kidde, I should just be able to hook black to black, white to white and red/yellow to red/yellow, no? ANy suggestions?

Thanks,
-DaG

I've been told that the life span of a smoke detector is typically 10 years. See www.smokesign.com
You should be able to connect black to black (120v ac power), white to white (neutral) and orange or red to orange or red (communications between smoke detectors). This is the typical wiring. No guarantee that it matches yours.
Please note that most manufacturers only want you communicating through
the same manufacturers equipment. So replace all with the same manufacturer.
Smokesign and other web sources can inform you on the different types
ionization or photoelectric.
You can also now buy at your local hardware store 10 year life batteries for smoke detectors.

Pkeegan has it right on. 10 years is the rule of thumb for replacing single-station smokes, especially Ionization technology.

System smokes of the type that connect to an alarm system are usually of better quality, and with cleaning and maintainance can last substantially longer.